Tested with latest LibreOffice and Thunderbird. When I call open file dialog ("open document", or "attach file") initially the open dialog is so small I can see around maybe 1.5 of the filename (I am referring here to height). As the result, I have to resize it _every time_. My suggestion how to solve it: remember the size and position of the file dialog (per app?) and next time it is called, start from the last position&size.
Gtk+ issue.