I don't know why I didn't see it previously, my problem seems similar to this... www.joomlapolis.com/forum/149-usage/231999-5641-admin-cannot-save-user-profile-in-backend?start=6

I'll look at what I'm using for validation for the name field...

Bingo!
Sure enough, it was "multiple words with spaces"... I changed that to "any string" and now, the buttons work!
I'm really not good with Regex... Any chance you could tell me what the correct expression would be to match any word with spaces, including French accents like é è à ê?

Thanks.