It seems incorrect to you "and" for contrasting verbs. "But" may be more fitting here than "and".
Both are accepted
I agree with you.
Is there always a comma before "a"?
Just like this one?
The comma always precedes the new clause
"You know but we don't know" is correct but not accepted. "We do not know" is stilted English. It's starting to get on my nerves that I have to write English that only a foreigner would use.