Thank you for your post.
Unfortunately, I am unable to replicate the problem on either Windows XP (SP3) or Mac OS X 10.5.8. This is what I have done.
1. In one of my test database files with 100+ records, I created a layout that had several fields.
2. I added a tab control, and added three tabs, making the second tab the default.
3. I placed a field in each tab control.
4. I go to Browse Mode, and the middle tab appears.
5. I use the "book" to browse the records, and I always stay in the middle tab. I also used keyboard shortcuts when I couldn't replicate with the "book".
Let me know what I'm doing differently from you, and I'll try to replicate the problem.