Yes, globals are incredibly powerful, but also dangerous. You have to be very careful not to accidentally move something otherwise it can cause major problems throughout all of the instances that are in use. I have brought this up several times and Dan has talked about adding some guardrails to possibly prevent this sort of problem.
My suggestion was that there needed to be some means of LOCKING a global against accidental movement. This would still allow you to edit properties but would prevent the accidental movements that can cause a reset.
I just found this bug yesterday. Built up a card with image and text area to use 12 times in a grid. Resize or move anything and every single one of them reverts. Very annoying.