Possible bugs should be reported in Report an Issue. The TS people from FileMaker that monitor that section need to know when there is such a change occurring.
When you report this over there, check the Windows Display control panel and let them know what percentage was specified and if changing the percentage (if you do not have it set at 100%) makes any difference. There have been a number of issues with this setting reported for FileMaker 13 and it could be that you are looking at a side effect produced by attempts to fix one or more of those issues.
I was looking for the "report an issue" choice but missed it. Got it posted there now. Thanks.