I found a reproducible sequence for this problem.

To reproduce:

Start workbench estudio and run estudio from within it.
Open existing project.
Undock Standard Buttons toolbar and dock at bottom of main window (all the way
   to the left).
Undock Project toolbar and dock at bottom of main window, to the right of
   Standard Buttons and in the same row.
Undock Standard Buttons toolbar and move it over left side of main window
   so that it docks there vertically but don't release mouse button.
Move Standard Buttons toolbar back down to dock it at bottom of main window.
Estudio crashes with violation of assertion `not_outside' of
   {SD_TOOL_BAR_ROW_POSITIONER}.on_pointer_motion.