You should really start trying these things when customers give you exact cases to reproduce.  Take your example here, and add the following right after line 69 ():

 

 

The tree that was added in the second editor completely disappears.  The contents of the "Links" dropdown in editor one is completely cleared out.  Comment those two lines out, and the two dropdowns appear correctly.  It sure looks to me like EditorWysiwygModeCss is affecting those things.