Not sure which version of IE your using so this probably isn't very helpful to you but my company exclusively used IE (version 7,8,9 predominantly with a little 10 thrown into the mix) with osTicket 1.6ST for years and I never received any reports of this issue nor experienced this issue myself. I'm guessing that perhaps its a setup thing.
We ran 1.6ST under IIS 6, and 6.5, and 7. The current version of PHP installed is 5.3.13 (although its been upgraded several times). We ran MySQL 5.0 and are currently running 5.1.