Most of the time, the Abilities panel expands vertically a little bit for me even though I always click to lock the interfaces. I customize and then click the lock so things won’t change.
I have it dragged out and next to the inventory (also dragged out). It always re-sizes itself to the size of that panel next to it.
This type of re-sizing happens when I log into the game. Everything’s fine until I logout and come back later.
I now think it might be happening after opening & closing the World Map.