Fix for #272 bug.

app/styles/editor/level/thangs_tab.sass

@@ -75,13 +75,14 @@
     right: 0
     top: 0
     bottom: 0
-    
+
     #thangs-list
-      position: absolute
+      position: relative
       right: 0
-      top: 40px
+      top: 0
       bottom: 0
       overflow: scroll
+      height: 100%
 
     h3
       margin: 0 -20px 0 0

app/templates/editor/level/thangs_tab.jade

@@ -22,7 +22,8 @@
     #canvas-top-gradient.gradient
 
 .add-thangs-palette.thangs-column
-  h3(data-i18n="editor.level_tab_thangs_add") Add Thangs
+  #thangs-header
+    h3(data-i18n="editor.level_tab_thangs_add") Add Thangs
   #thangs-list
     for group in groups
       h4= group.name

app/views/editor/level/thangs_tab_view.coffee

@@ -90,12 +90,19 @@ module.exports = class ThangsTabView extends View
     context.groups = groups
     context
 
+  onWindowResize: (e) ->
+    $('#thangs-list').height('100%')
+    thangsHeaderHeight = $('#thangs-header').height()
+    oldHeight = $('#thangs-list').height()
+    $('#thangs-list').height(oldHeight - thangsHeaderHeight)
+
   afterRender: ->
     return if @startsLoading
     super()
     $('.tab-content').click @selectAddThang
     $('#thangs-list').bind 'mousewheel', @preventBodyScrollingInThangList
     @$el.find('#extant-thangs-filter button:first').button('toggle')
+    $(window).resize @onWindowResize
 
   onFilterExtantThangs: (e) ->
     @$el.find('#extant-thangs-filter button.active').button('toggle')
@@ -131,6 +138,9 @@ module.exports = class ThangsTabView extends View
     @thangsTreema.open()
     @onThangsChanged()  # Initialize the World with Thangs
     @initSurface()
+    thangsHeaderHeight = $('#thangs-header').height()
+    oldHeight = $('#thangs-list').height()
+    $('#thangs-list').height(oldHeight - thangsHeaderHeight)
 
   initSurface: ->
     surfaceCanvas = $('canvas#surface', @$el)