This is how the tabs look when recalling the same layout with build 820 to current build 832. The tabs that are not locked are missing. Recreating the tabs and saving under a later version does not solve the problem. Again, this is a dual panel layout and the problem is on the left panel. The right panel works as expected with the non-locked tabs displayed and a single panel layout works okay too.
The only current fix is to lock all the tabs. But since it once worked properly, I'm hoping it can again.