This often happens when someone tries to re-anchor a control without clearing the old anchors first.
E.g. Addon A tells the control to stick to point A with the top-left corner and to point B with the bottom-right. Then Addon B comes along and suddenly tells it to stick to point C with the top-left corner which is ok as it will just override the previous value, but instead of the bottom-right it chooses the top-right corner for point D, which makes the control go "AaaaaaAAAAhh!!! I'm a rectangle! I can't stick to 3 different points like that! What do you want from me?! Leave me alone!!"
