Yes, I've hit the exact same issues with URLStream (even when the connections are properly closed). I never found a satisfactory workaround.
What did you end up doing? As much as I wish we could require all our customers to move away from
IE, it is not a viable option. Any input will be appreciated.
Mostly, we just documented it as a known issue; fortunately, that was feasible for us. Our customers don't typically open and close many new windows of our app, so it's not the end of the world.
When I dug into this, I saw some pretty bizarre behavior from IE: even when you close the underlying Socket and you see the appropriate FIN TCP wire messages, IE would *still* not let Flex open new connections to the same host. This persisted until you restarted not only the current browser, but all IE instances. The connection book-keeping is somehow totally fubared.
What we *considered* doing but ultimately determined to be impratcical was to only have the main application open these connections, and the other instances marshall their network communication through the main app using LocalConnection. In theory, this should work, but it's likely to be very awkward.