res_fax ReceiveFax(...) creating unreadable files

I have recently created a virtualized Asterisk 1.8 Cent 5 machine, running in VMWare. This specific machine is only concerned with sending and receiving faxes. Sending faxes seems to work fine, but I have been getting some reports of ReceiveFax() generating unreadable files. I asked for examples and was forwarded multiple PDFs that were simply unopenable. When trying to open Adobe throws some error about the file being corrupted.

I know there have been timing issues associated with Asterisk when running virtualized, but was not sure if res_fax too was affected. Has anyone had issues like this? Can timing issues result in trashed ReceiveFax() output?