CUPS thinks PowerPoint file is type text/plain

[John Five]

Hi, I manage a CUPS server for about 150 printers at a Univeristy. We
have a situation where a user tried to print various PowerPoint files
and some were detected by CUPS as being text/plain.

In these cases the files were printed as plain text instead of the
actual slides and images contained in them. Needless to say this is
causing one of our printers (an HP Color LaserJet 4700 with latest PS
PPD installed) to spew out countless pages of plain text/binary data.

What do I do in situations like this when files that are clearly not
plain text are detected as such. Who is the culprit in this situation?
The document itself, the print driver on the client, the print driver on
the server, outdated version of CUPS, etc..?

Has anyone else experienced this problem or similar problems? How does
one go about making CUPS not think binary print jobs are plain text?

Thanks in advance for any help on this topic.