Could you be more accurate?
You place the shape, it goes somewhere. You go to click the validation button and by the time you do it, the shape has moved?
I am not completely sure how we could fix that. An extra "Are you sure?" seems too much. There is surely a better way to deal with the issue. Maybe we could disable the OK button if the shape has moved in the last 300ms or something.
In the short term, maybe zooming in may help lower the frequency of this happening? The bigger the grid, the more chance you have to be correctly placed with no rounding effects.
May I ask what phone you are playing on? Are they fast or old/slow?