Have you downloaded and installed the v2 updater for FileMaker 11?
A similar scrolling bug was reported and since has been reported as fixed with the release of the update.
For More Information see: Filemaker 10 Advanced Crashes when scrolling long scripts at random
This is one of many acknowledged bugs that can be found in the Known Bug List here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: http://www.4shared.com/file/8orL8apk/FMP_Bugs.html