File uploaded to a regular dir and then SIZE doesn't find it? This the same login as uploaded the file? I wouldn't think that should be possible unless the file wasn't uploaded but extracted like a .nfo/.diz or something. On the other hand, if it was uploaded by a different user you'll have to pay attention to the timestamps carefully... Any chance it was it in the process of being uploaded in another login at the time?
On the other hand, it's possible I missed marking the directory as dirty somewhere with all the changes in v7.6 but I'd need more details, you can PM me logs if you think it shows the problem clearly. BTW, anyone can force ioFTPD to re-cache a directory using 'site refresh' to see if that makes the problem go away.
Does this happen for more than 1 file in a directory?