Thank you for the post.
I am not able to reproduce this behavior using a tab control (4 tabs) inside a tab control (4 tabs) with 4 pop-up menus on every tab. If possible, I would like to take a look at your file. Check your inbox at the top of this page for instructions on how to submit your file.
Hmmm. I know that I've seen that odd triangle result before, but can't pull up anything that fits....
I have had this issue before. Simply create a new object in the desired style and then copy that style to the existing object. This will fix it permanently.
Can you list the specific elements that result in this appearance? Do you concur that it has to be a field located in a tab control or does this actually have nothing to do with the resulting appearance for the field?
It could be related to the tab menu. My app has pop-up menus in tabs as well. If I remember correctly I actually created a new pop-up menu outside of the tab object on a new empty layout to copy the style and fix the display issue. I simply assumed that it was related to a conversion error of an older FM 11 solution.