[eluser]WanWizard[/eluser]
I've been discussing this issue with one of my business partners, a long time MS expert.
He said he'd seen this before, the issue might be that IIS never sends an RST at the end of the transmission, so the browser thinks there is more data coming. Depending on the browser you have to wait for the TCP session to timeout, which can be several minutes.
Can you check what your server timeout values (ConnectionTimeout, HeaderWaitTimeout, and MinFileBytesPerSec) are?