As Earrindo says, anything you have already placed, during the trial period, will remain.
Unless you try to move it, or remove it, when you won't be able to put it back down, or replace it with something else.
So, make sure it's perfectly placed, during the trial period, basically.
Also, make sure the last thing you place/move is something you don't mind if it moves slightly, due to the bug.
As that item/group seems to be the thing that will be most likely to move on its own.