You just have to be careful and more aware when you go into the workbench room. Try to press "Fix" as quick as possible. Also, you might want to sweep the walls of the room before crafting because I've noticed that people love to hid in there and wait for you to do your little hand motion before going up to you.
Also, try to act like you are about to craft something, but then look around and see if someone tried to come up to you, and if they do, then quickly move out of the way.
Btw, if the (thief) thing come up on their heads, it means that you are still safe because they were unsuccessful in stealing from you.