Thank you for your post.
I am unable to replicate the issue with FileMaker Pro 15.0.1 under both Windows 7 and Mac OS X 10.11.5. Here are my specific steps:
1. I created a new database file "Test.fmp12".
2. I created a Text field "Name".
3. I added one record and entered "TSGal".
4. I activated Script Workspace and created a script "Test" with the script step:
Show Custom Dialog [ "Test" ; "Test" ]
5. I saved the script and executed it to make sure it works (it does).
6. I switch back to the database and searched for "TSGal". The record is found.
7. I press Ctrl-R, and I'm back in Find mode.
8. I changed the find criteria to "hschlossberg", pressed return, and I get the expected "No records match this find criteria" dialog. I cancel out, press Ctrl-R, and I'm back in Find mode.
Let me know what I'm doing differently than you so I can replicate the issue.
Do you have any custom menus active? Do you have any plug-ins installed/enabled?
Argh. I couldn't shake it yesterday on a couple different files, but I didn't try a restart. Today I can't replicate it, but the only reason I reported it yesterday was that it has been happening a lot lately. CTRL-R was an example, but (when the problem happens), similar happens after a find with CTRL-up and CTRL-down (moving script steps around instead of navigating records).
I'll continue to monitor for it and next time check things like custom menus, other windows that are open, other files, etc.