Since v3.2 I get the following behavior. If the open B4A and the project and then the designer all is well. If I close the designer and then reopen it I get prompted right away to save changes. Behind the prompt there doesn't seem to be anything loaded and I worry that I've lost my design. If I click no the designer opens with the saved design. If I close B4A and reopen the process repeats. I don't care to click yes and see what happens!
I've noticed this pre 3.2 sometimes as well. It can be scary and I never click yes. In your case if it's a pre 3.2 project then I suspect it's related to the new designer version adding things therefore marking it dirty. In this case I don't think you have much choice but to say yes.
If I click yes it saves a blank layout. If I would keep the same name I would loose the current layout. So for some reason it opens a blank layout even though I already have a layout and asks to right away to save it.