I'm running an up-to-date, un-modded install of phpBB 3 and have an odd attachment problem.
I have max attachment size set to 48 MiB and have no problem with files up to about 8 MB.
Trying to upload any file larger than that reloads a new, blank "new topic" page after you click the "add the file" button - any text in the subject and body fields is gone and you're back to square one.
If it was a legitimate file-size error I'd think that there would be a "your file is too big" message and the filled-in fields wouldn't be cleared, right?
Is there a setting I'm missing somewhere?