Hi,
there is no POST capable browser in 1.4.1; whose code are you using ?
You can try my web server if you please (lookup lwHTTPd in this list or google it/me), however, I don't think your are chasing the bug in the proper way.
Your browser should not crash... the server should not care about the file type.
Did you capture the traffic ?
Where are you (or the server) storing the data coming in ?
What happens in the embedded (lwIP) system when the transfer halts ?
If the server is OK, you are mishandling memory in your application, your piece of code called back from the POST handler. However, since that server is not a lwIP application, I would not rely on it.
Plus, ST is starring many bugs this week...