Feng 1.7.2 and below does not use all the IMAP functions really. It's behaving like it's POP3. Even when you select IMAP, it will behave like you have connected with POP3.
Feng Office needs to implement some real IMAP functions. Like you said, if it's marked "read" on server, it should be marked "read" in Feng. If it's deleted from server, it should be deleted from Feng. And so on..