I ran into the exact same issue. I did some quick investigation, about 5 minutes later I knew where the issue was.
It's really sad to see that nobody was able to answer this question, but for what it's worth:
The maximum upload filesize is gathered from a few settings in .ini files belonging to php. I checked the code of dokuwiki and found out the following:
$post = (int) php_to_byte(@ini_get('post_max_size'));
$suho = (int) php_to_byte(@ini_get('suhosin.post.max_value_length'));
$upld = (int) php_to_byte(@ini_get('upload_max_filesize'));
if($post && ($post < $okay || $okay == 0)) $okay = $post;
if($suho && ($suho < $okay || $okay == 0)) $okay = $suho;
if($upld && ($upld < $okay || $okay == 0)) $okay = $upld;
I think you have the exact same issue is I did: running php with the suhosin patch. In that case, you can change the post_max_size and upload_max_size as much as you want, it won't make any difference here, because the value of suhosin has priority if it is lower.
I'm running dokuwiki on Debian and found the config files containing "suhosin.post.max" as follows:
root@vhost01:/etc/php5# grep -rli 'suhosin.post.max' *
apache2/conf.d/suhosin.ini
cli/conf.d/suhosin.ini
conf.d/suhosin.ini
In these files, you can change the suhosin.post.max_value_length value, by removing the ; character in front of it.
Original (~1 Megabyte):
;suhosin.post.max_value_length = 1000000
Updated (64 Megabyte in Bytes):
suhosin.post.max_value_length = 67108864
(remember to remove the ; in front of this setting)
Important:
I'm running on Debian, I only had to change /etc/php5/apache2/conf.d/suhosin.ini.
Don't forget to restart apache2 after making the changes.