I noticed a quirk with a string that had the option "display as background" checked. A not the string overlapping active underneath got partially invisible by changing the string to another paragraph. Lining up with one border of the string.
This second paragraph was not longer than the first one. And, as told, the active didn't even overlap the string, which could be the troublemaker.
I turned off the "display as background" option then. And now it works. But that's a slower way of displaying the string, isn't it?
Sidenote: it is a pain to work with string when using it on an area with a predefined size and several paragraphs. I always have to run the game, enter the needed paragraph, and have a look if it still fits to the field i want to display it at. I hope that there will be a solution for in the future. A way to display different paragraphs of one string in the frame editor would be a fabulous thing to have
MMF2 Dev, latest Build 243