Thank you for your post.
I am unable to replicate the issue using FileMaker Pro 14.0.3 under Mac OS X 10.10.5 (and 10.11.1). Here are the steps I took:
1. I created a database file with three Text fields: Field1, Field2, Field3
2. I added a button that executes the Single Step "Show Custom Dialog".
3. I created three more Text fields: Field4, Field 5, Field6
4. I went to Browse mode, and entered one record with sample data. The tab order skipped over the button.
5. I returned to Layout Mode, changed the tab order so the button is in the fourth position. I returned to Browse mode to verify the tab order worked (it did).
6. In Layout Mode, I set a Hide object when condition to: IsEmpty (Field6)
7. Returning to Browse mode, I created a new record, and the button was not present (as expected). I tabbed through, and I was unable to tab to the hidden button.
Let me know what I'm doing differently than you so I can replicate the issue.
Thanks for the reply, TSGal. I doublechecked and found my Hide condition didn't cover enough cases. When I fixed it, Tab Order worked fine. Please consider this closed. My error.