Wow, netfront really sucks.
Does putting a trailing slash on the end (eg. http://4-ch.net/dqn/mobile/ ) cause the same problem?
I'm rather curious as to what strange headers netfront is sending. Do you see anything unusual in http://services.4-ch.net/tools/headers.pl ? That stupid browser shouldn't be getting confused over a differing "Content-Location" header in a 200 response, right?