1. Organise Scene, Asset Store, Animation and Game and windows as displayed on the screenshot
(Scene, Asset Store and Animation set as tabs, Game windows is placed near separately)
2. Start to close one by one Animation tab, then Asset Store tab, then Scene tab

Actual result:
When Unity keeps place for closed tabs instead to resize remaining window (Game window) errors appear in console: ArgumentOutOfRangeException: Argument is out of range.

Log is attached

ArgumentOutOfRangeException: Argument is out of range.
Parameter name: index
System.Collections.Generic.List`1[UnityEditor.EditorWindow].get_Item (Int32 index) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Collections.Generic/List.cs:633)
UnityEditor.DockArea.OnGUI () (at /Users/builduser/buildslave/unity/build/Editor/Mono/GUI/DockArea.cs:326)

Is a regression:
Is not reproducible on:
Version 5.4.1p3