I’ve noticed several times now, if I create a new longpress key, and add a character to it either by dragging a character into it from the character map, or double clicking the character in the character map, Developer handles this fine.
But if I have one character in a longpress key, then attempt to replace it with another character, dragging or double clicking the new character does not fully replace the previous character. The ID line still has the code from the first character. For example, I created a key and dragged U+0257 (d with hook) to it. Then I dragged 1D81 (d with a hook at the bottom of the letter) into that key, and my ID line still shows 0257.
I don’t think that changing the ID field is automatic.
Perhaps you’d like to propose that this be a new feature for Developer? (Or maybe it’s already in the queue.) But perhaps it should be a dialog that asks whether you want the ID to change to match the Text and/or Unicode fields?