Operating System ver? (appears to be OSX) FMP ver? Database is local or remote? Computer make and model? Does the same thing on other computers?
Resizing the window does not change anything? Resolution on monitor? Change this does what?
Client on OSX Mavericks 10.9.1 using Filemaker 13.0v1
Computer is MacBook Pro 17 inch, Early 2011 with Intel HD Graphics 3000 512 MB, 8 GB 1333 MHz DDR3, 2.2 GHz Intel Core i7, OS X 10.9.1 (13B42)
Always used remote, Tested with local copies of both known occurrences and neither databases do this when opened local.
Server is this pictured instance is Filemaker Server 13 running server 2008 occurs as well in a separate database just as large and complex but completely different in Filemaker Server 12.4 running on Windows server 2008
I have never resized window but will do so on next occurring which is next week when connecting to these files and will resize and report.
This sounds like something to post over in Report an Issue.