There was a bug in previous versions of fltk that caused windows to shrink every time the window was closed and reopened (but it would correct itself if the window was moved). Fltk 1.3.3 fixes this bug, so if the window shrinking bothers you, feel free to upgrade to 1.3.3. We will use 1.3.3 for future projects.
Install fltk-1.3.3. Refer to instructions here if you are having trouble.
Open your .vcxproj file with Notepad++ or your preferred text editor, and perform a find/replace with 1.3.2/1.3.3 respectively. You should be good to go!