That is a bug, or at least a very poor implementation of a software feature. Lots of people have been complaining about that and let us pray Serif fix it in the next release of Designer. It is really naff at the moment and lets the whole program down.
Solutions (sort of).
A. Use the Transform panel and swipe across the X or Y controllers to move it.
B. Draw a larger shape (like a rectangle) and select that and the small object. You can then use the larger shape as a handle to move the smaller shape. A bit of a bodge but it works quite well.