Bug#677086: apache2-mpm-prefork: apache2 sends "400 bad request" on POST from some firefox browsers

[Thomas Voelkl <thomas@puzzleandplay.de>]

I have collected some statistical data (by analysing the apache logs) on 
how often this problem occurs on our webserver:
~38% of our users upload files by using a firefox browser
~6% of these firefox users get the error (400 bad request) when 
uploading a file

bash-command:
cat access.log | egrep '"POST .+" 400 ' | cut -d ' ' -f 2 | sort -u | wc -l

By using this command you see the amount of unique users having that 
problem. And I think 6 out of 100 firefox-users are too much users to 
ignore that problem.

Remember: When changing apache from 2.2.16 (squeeze) to 2.2.22 (wheezy) 
that problem does NOT occur anymore. So, what changes in apache from 16 
to 22 can be responsible for that strange behavior?

Thanks,
Thomas