Thank you for your post!
I was able to reproduce this on Mac OS X 10.10.5 with FileMaker Pro 15.0.1 with both a Hosted and Local copy of the file. This issue does not seem to occur on Windows. To reproduce I followed these steps:
1. Created "test.fmp12"
2. Created New Script "Test"
3. Created 315 lines of Set Variable Scripts
4. Quickly hit Return and type "GTL" for go to layout and it input "tlg"
I am sending a report to Testing and Development. I will post back here when further information is available.
This issue has been addressed in FileMaker Pro 16.