This setting allows for a 100x100 (width by height). If you use a capital X...width is zero and height it blank.
Same problem for "Maximum Display Avatar Dimensions" setting too.
Easy fix would be strtolower before input to database.
Would be nice if PHP had a case insensitive explode()
Thank you for your bug report.
This bug has been fixed in our internal code repository. Please note that the problem will not be fixed here until these forums are updated.
With regards,
MyBB Group
Revision 4254
This fix is incomplete. The problem still appears in the memberlist.
In memberlist.php find:
list($max_width, $max_height) = explode("x", $mybb->settings['memberlistmaxavatarsize']);
Replace with:
list($max_width, $max_height) = explode("x", my_strtolower($mybb->settings['memberlistmaxavatarsize']));
Ah, that was a completely separate setting