Thank you for your post.
This is a continuation of the thread:
Try installing a trial version of FileMaker Pro 12 on your machine. Convert your file to FileMaker Pro 12 (your original file remains intact, as the new file reads your old file and creates a file with .fmp12 extension), and try to replicate the issue. This will give me a better idea if the problem is sytem related or FileMaker Pro 8.5 related.
Also, if you have access to another machine, try installing FileMaker Pro 8.5 on the second machine and see if the problem is reproducible. This will let me know if it is machine related.
In the future, use the Post A Answer box at the bottom of your screen to post follow up questions, etc and you will be able to build a "thread" of questions and responses on your issue. That makes it easier for others to read and understand the full context behind your posts.