Setting Workspace.SignalBehavior to Deferred causes the UI editor’s dragging feature to become “sticky”.
This first happened to me a couple weeks ago (don’t know when exactly) but can be reproduced 100% of the time.
Reproduction Steps
Set Workspace.SignalBehavior to Deferred.
Select any GuiObject.
Click the viewport to deselect the gui.
The resize handles will remain on screen.
Select another gui.
The last selected gui will “stick” to your cursor.