What's wrong with Thunderbird

[Jim]

I have had on three different users where the email get so scrambled up, 
you can get a email and it's from 2 different people that you know on 
the same email, a case where you could only get email from scam site. 
there's no set pattern as how the emails come in. The out going email 
shows as normal.

I have pulled their address book and deleted Thunderbird and 
.thunderbird in home directory.
reinstalled Thunderbird and put the address book back in .thunderbird 
and every incoming email is normal.
Thunderbird is going Bonkers.