HP LaserJet 602 envelope feeder(CE399A)

Anyone have any luck getting one of these feeders to function correctly?

this one in particular:

http://store.hp.com/webapp/wcs/stores/servlet/us/en/hp-laserjet-75-sheet-envelope-feeder?jumpid=ba_r...=

We have several, but only 2 will actually print an envelope without the user having to press "OK" on the printer panel. We have tried firmware updates, reinstall etc. Will "seem" to be fixed for a short time, then bam! right back to non working.

Read several lengthy threads on HP website to no avail.

I love how they mention "Increased Productivity" as one of its selling point. :/