You got me thinking, and it might have actually been a different keyboard and not my Ajazz (I did have a similar Chinese one at the time) I was having that problem with... However, it was indeed the problem I've described.
The plate was raised way above the switches and mounting "normal" keycaps was possible but it would not actuate due to the "skirt" hitting the plate and preventing further travel of the raised stem.
I don't know what keyboard you're talking about but that sounds really weird...
Most keyboards have plates, even if they're not a floating key design where the plate doubles as the top housing they're still there. MX switches (assuming they were MX switches...) are designed to mount into plates in only one position. If they somehow positioned things so that the plate was above the normal mounting point then the plate wouldn't actually be doing anything because it wouldn't be holding the switches in place.
So either:
1. It was a super-thick plate that extended significantly higher than a normal plate. But why would anyone do that, especially cheap Chinese keyboard makers since it would increase material costs with no real benefit?
2. They weren't MX switches at all (could still have an MX-compatible mount though). But even then most switches are designed similarly so I don't know what they would be...
3. You're misremembering something.