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There has been a fix so that floating windows would no longer float off
the screen by accident, but would stop at the edge of the screen. This
is in the source code, and that's causing the behaviour that you see in
the version created from source. Probably this fix had not yet made it
into the crosswire repository. If you'd like to work on the code for
moving the window, that would be nice. It's in floatingwindow.cpp.
Wishing you well, Teus.