This happens with dimensions on a drawing, and pmi dimensions. More often than not, when you want to add appended text, while placing the dimension, nothing will enter into the quick pop-up appended test input area. You have to go to the "edit appended text" window.
We have had this happen with at least 2 users, including myself. I've had it work, go to the next dimension, and not work. Once it quits, it's done. I've been able to capture it not working on video, and submitted an IR to GTAC, but they can't reproduce it.
Curious if anyone else has run into this, and if so, have you found a pattern to way to trigger it?