Looks like I stumbled on a bug with inline popup regions when they have items that open some sort of content (e.g. datepicker or popup lov)
After the item's content/dialog is opened, it doesn't seem to be able to know when the item loses focus (so that it can close gracefully).
Which results in the content/dialog to remain visible and unusable.
The issue seems to go back at least to APEX 22.1 (I haven't tested earlier versions).
Searching the forum, I found a similar issue reported back in 2021 (https://forums.oracle.com/ords/apexds/post/apex-21-1-4-popup-lov-in-modal-dialog-issues-8032).
It's pretty much the same issue but for inline dialog. That one was fixed, but not the inline popup.
@anthony-rayner-oracle
I've also built a simple app showing the issue:
https://oracleapex.com/ords/r/max_playground/test-inline-dialog