I am facing a similar issue that began to occur after the Meta Box AIO 3.2.0 update (or at least that is when I noticed it). Only for me, I don't have an email field. I have four required fields and I am requested to enter something in the first and last required fields in order to save any changes to the custom fields metabox.
Interestingly, it only requests it for 2 out of the 5 required fields I have. Those two fields are "text" type fields, the others area text area and dropdowns.
It does not actually "save" the inputs from what I can see, it just requests saving similar to what the original poster described (and showed in their video). It does not affect saving or the custom fields from working, but it is annoying to have to enter in something random every time I edit my fields and save.