We had one quite interesting problem at work.
We had a Drupal site where we couldn’t upload files larger than 32 MB, while having in php.ini :
upload_max_filesize = 200 MB post_max_size = 200M
After disabling APC, we could upload larger files.
It turns out, it seems changing the following in apc.ini
fixed the problem.
Doc : http://www.php.net/manual/en/apc.configuration.php#ini.apc.rfc1867-freq
<code>apc.rfc1867_freq string The frequency that updates should be made to the user cache entry for upload progress. This can take the form of a percentage of the total file size or a size in bytes optionally suffixed with "k", "m", or "g" for kilobytes, megabytes, or gigabytes respectively (case insensitive). A setting of 0 updates as often as possible, which may cause slower uploads.</code>
I’m pretty sure this should not be related, as I have apc.rfc1867=0 in apc.ini.
If someone has a clue, drop me a line :-)