Bizarre Mail.app behavior

I recently added my work e-mail account (POP) to mail.app. I was already using mail.app for two other gmail accounts (IMAP).

The issue: when I send e-mails from my work address, the replies are coming through to my gmail account instead of back to my work account. To "reenact" I played around and sent an e-mail from my work address to my personal gmail address (all through mail.app). Once I receive the mail in the gmail account, the "From" field lists the e-mail coming from my gmail account instead of my work account - ie the account I sent it from.

I don't have any forwarding turned on and cannot find a connection between my work account and gmail account in the settings.

Has anyone experienced anything similar to this? It's getting frustrating having all of my work e-mails somehow redirected over to my personal account.

Thanks in advance-
Chris