I was able to reproduce this in Access 2016 32 bit. I've never used that part of the subform wizard. I've always created my subforms as a named form first then used the existing form option.
Microsoft is constantly issuing patches for its products. They are not defective, every software product has bugs. I've never seen this one reported before. I would suggest reporting it at access.uservoice.com. But frankly, I doubt if this will be given much priority.