diff --git a/app/assets/javascripts/workers/worker_world.js b/app/assets/javascripts/workers/worker_world.js
index 171cb0be8..a9d998fac 100644
--- a/app/assets/javascripts/workers/worker_world.js
+++ b/app/assets/javascripts/workers/worker_world.js
@@ -478,6 +478,7 @@ self.onWorldError = function onWorldError(error) {
   else {
     console.log("Non-UserCodeError:", error.toString() + "\n" + error.stack || error.stackTrace);
     self.postMessage({type: 'non-user-code-problem', problem: {message: error.toString()}});
+    return false;
   }
   /*  We don't actually have the recoverable property any more; hmm
   if(!error.recoverable) {
diff --git a/app/lib/simulator/Simulator.coffee b/app/lib/simulator/Simulator.coffee
index 8b8f9f92f..6f86fa6a3 100644
--- a/app/lib/simulator/Simulator.coffee
+++ b/app/lib/simulator/Simulator.coffee
@@ -5,7 +5,7 @@ GoalManager = require 'lib/world/GoalManager'
 God = require 'lib/God'
 {createAetherOptions} = require 'lib/aether_utils'
 
-SIMULATOR_VERSION = 2
+SIMULATOR_VERSION = 3
 
 simulatorInfo = {}
 if $.browser
@@ -334,6 +334,7 @@ module.exports = class Simulator extends CocoClass
       calculationTime: 500
       sessions: []
       simulator: @simulator
+      randomSeed: @task.world.randomSeed
 
     for session in @task.getSessions()
       sessionResult =
diff --git a/app/lib/world/world.coffee b/app/lib/world/world.coffee
index 538f4976a..37d304f5d 100644
--- a/app/lib/world/world.coffee
+++ b/app/lib/world/world.coffee
@@ -360,7 +360,7 @@ module.exports = class World
     #console.log "... world serializing frames from", startFrame, "to", endFrame, "of", @totalFrames
     [transferableObjects, nontransferableObjects] = [0, 0]
     delete flag.processed for flag in @flagHistory
-    o = {totalFrames: @totalFrames, maxTotalFrames: @maxTotalFrames, frameRate: @frameRate, dt: @dt, victory: @victory, userCodeMap: {}, trackedProperties: {}, flagHistory: @flagHistory, difficulty: @difficulty, scores: @getScores()}
+    o = {totalFrames: @totalFrames, maxTotalFrames: @maxTotalFrames, frameRate: @frameRate, dt: @dt, victory: @victory, userCodeMap: {}, trackedProperties: {}, flagHistory: @flagHistory, difficulty: @difficulty, scores: @getScores(), randomSeed: @randomSeed}
     o.trackedProperties[prop] = @[prop] for prop in @trackedProperties or []
 
     for thangID, methods of @userCodeMap
@@ -467,7 +467,7 @@ module.exports = class World
             w.userCodeMap[thangID][methodName][aetherStateKey] = serializedAether[aetherStateKey]
     else
       w = new World o.userCodeMap, classMap
-    [w.totalFrames, w.maxTotalFrames, w.frameRate, w.dt, w.scriptNotes, w.victory, w.flagHistory, w.difficulty, w.scores] = [o.totalFrames, o.maxTotalFrames, o.frameRate, o.dt, o.scriptNotes ? [], o.victory, o.flagHistory, o.difficulty, o.scores]
+    [w.totalFrames, w.maxTotalFrames, w.frameRate, w.dt, w.scriptNotes, w.victory, w.flagHistory, w.difficulty, w.scores, w.randomSeed] = [o.totalFrames, o.maxTotalFrames, o.frameRate, o.dt, o.scriptNotes ? [], o.victory, o.flagHistory, o.difficulty, o.scores, o.randomSeed]
     w[prop] = val for prop, val of o.trackedProperties
 
     perf.t1 = now()
diff --git a/app/schemas/models/level_session.coffee b/app/schemas/models/level_session.coffee
index 41f585f43..2d4c74405 100644
--- a/app/schemas/models/level_session.coffee
+++ b/app/schemas/models/level_session.coffee
@@ -286,6 +286,7 @@ _.extend LevelSessionSchema.properties,
                 type: ['string', 'null']  # 'null' in case an opponent session got corrupted, don't care much here
                 description: 'What submittedCodeLanguage the opponent used during the match'
         simulator: {type: 'object', description: 'Holds info on who simulated the match, and with what tools.'}
+        randomSeed: {type: 'integer', description: 'Stores the random seed that was used during this match.'}
 
 c.extendBasicProperties LevelSessionSchema, 'level.session'
 c.extendPermissionsProperties LevelSessionSchema, 'level.session'
diff --git a/app/views/ladder/MyMatchesTabView.coffee b/app/views/ladder/MyMatchesTabView.coffee
index 873875d27..327335b31 100644
--- a/app/views/ladder/MyMatchesTabView.coffee
+++ b/app/views/ladder/MyMatchesTabView.coffee
@@ -82,7 +82,7 @@ module.exports = class MyMatchesTabView extends CocoView
         stale: match.date < submitDate
         fresh: fresh
         codeLanguage: match.codeLanguage
-        simulator: JSON.stringify(match.simulator)
+        simulator: JSON.stringify(match.simulator) + ' | seed ' + match.randomSeed
       }
 
     for team in @teams
diff --git a/headless_client.coffee b/headless_client.coffee
index 27fca376b..7db937737 100644
--- a/headless_client.coffee
+++ b/headless_client.coffee
@@ -95,6 +95,7 @@ GLOBAL.Backbone = require bowerComponentsPath + 'backbone/backbone'
 unhook()
 Backbone.$ = $
 require bowerComponentsPath + 'validated-backbone-mediator/backbone-mediator'
+Backbone.Mediator.setValidationEnabled false
 GLOBAL.Aether = require 'aether'
 # Set up new loader. Again.
 hook()
diff --git a/headless_client/worker_world.coffee b/headless_client/worker_world.coffee
index 981266376..f32928f28 100644
--- a/headless_client/worker_world.coffee
+++ b/headless_client/worker_world.coffee
@@ -148,7 +148,9 @@ work = () ->
         self.postedErrors[errorKey] = error
     else
       console.log 'Non-UserCodeError:', error.toString() + "\n" + error.stack or error.stackTrace
+      self.postMessage type: 'non-user-code-problem', problem: {message: error.toString()}
       self.cleanUp()
+      return false
     return true
 
   self.onWorldLoadProgress = onWorldLoadProgress = (progress) ->
@@ -178,8 +180,8 @@ work = () ->
 
 codeFileContents = []
 for codeFile in [
-    'world.js'
     'lodash.js'
+    'world.js'
     'aether.js'
     'app/vendor/aether-clojure.js'
     'app/vendor/aether-coffeescript.js'
diff --git a/server/queues/scoring.coffee b/server/queues/scoring.coffee
index c2cf71be4..66a947ce8 100644
--- a/server/queues/scoring.coffee
+++ b/server/queues/scoring.coffee
@@ -15,7 +15,7 @@ bayes = new (require 'bayesian-battle')()
 scoringTaskQueue = undefined
 scoringTaskTimeoutInSeconds = 600
 
-SIMULATOR_VERSION = 2
+SIMULATOR_VERSION = 3
 
 module.exports.setup = (app) -> connectToScoringQueue()
 
@@ -611,6 +611,7 @@ updateMatchesInSession = (matchObject, sessionID, callback) ->
   currentMatchObject.opponents = opponentsArray
   currentMatchObject.codeLanguage = matchObject.opponents[opponentsArray[0].sessionID].codeLanguage
   currentMatchObject.simulator = @clientResponseObject.simulator
+  currentMatchObject.randomSeed = @clientResponseObject.randomSeed
   LevelSession.findOne {'_id': sessionID}, (err, session) ->
     session = session.toObject()
     currentMatchObject.playtime = session.playtime ? 0