When selecting all text in a document using CTRL-A, it's currently 
impossible to deselect it using the mouse. All actions are
considered as 'move' instead of using a single left-click as 'place
cursor here' command.

Configuration error or should I file a bug report/feature request?
      

This is a known bug in Scintilla and there is a (at least partially)
fix in Scintilla CVS. I think before the next Geany release we will
include the fix (hopefully Scintilla 1.74 is out in the meantime).

A bug report for this already exists:
https://sourceforge.net/tracker/?func=detail&atid=787791&aid=1727228&group_id=153444

Will be fixed soon.
    

Shoud be fixed in SVN r1629.
The included Scintilla component was updated to 1.74 which contains a
fix for this problem.

Regards,
Enrico