You're probably right. I was pretty sure I'd read at least one case about someone with the 80% problem switching chargers and then it would go up to 100%. However, going back and reading a thread about it again, I see in that case it was ultimately diagnosed as a battery problem.
Maybe I was just confusing a couple battery related issues.
Odd behavior with buttons and other similar issues during charging do seem to be related to non-standard chargers though.