It was tough, but I have finally reproduced this bug with a relatively short
sequence.  It needs to be added to the Critical Bugs list.  This crashes every
time for me, so please contact me for clarification if you cannot reproduce
this.  To reproduce:

Delete ~/.es directory.
Compile sample graphical application.
Minimize APPLICATION Editor tab.
Save layout as "weasel".
Undock Output tab and dock along on right side of main window.
Auto Hide Feature tool.
Undock Class tab and dock along top side of main window.
Undock zone with Feature Relation tabs etc and dock along left side of
   main window.
Auto Hide Clusters tab.
Maximize APPLICATION Editor (two clicks may be required).
Save layout as "turkey".
Reset tools layout.
Open layout "turkey".
Open layout "weasel".
Undock Feature window on left side - Feature gets beige background (theme
   color) and does not undock.  At this point, things are screwed up.

Undock Feature window from left side and dock along right side of main window.
Undock Feature window from left side and dock along right side of main window.
Undock Feature window from left side and dock along right side of main window.
Estudio crashes with seg fault in {SD_NOTEBOOK}.select_item (trace
   previously attached).