Why would BlackBerry email setup process mis-identify IMAP server as POP?

I have a user trying to set up a Curve 8310 device to read Exchange mail via IMAP. User enters all pertinent info (tried both device & web interface): email address, username, password and IMAP email server but gets this BIS error: “This POP server is not supported as it does not have sufficient capabilities. Please try a different POP server.” But I know the server is IMAP because my work (a university) doesn’t even do POP servers anymore.
User is able to set up other IMAP email accounts without incident.
I’m at a loss for an explanation. AT&T, RIM and my system administrators have been of no help.