any parent transformations are passed on to the children, it sounds like the locator had transformations on it, and when you un-parented the object the parent transformation was removed
There's a setting in the "unparent" options (which is basically what you're doing here - unparenting a node) which tells it to preserve local transformations or not. This can prevent objects "jumping" when you move them - instead it just adjusts their relative transform values so they appear in the same place.