I recently installed the Mac OSX 10.10 Yosemite update. Immediately after, my HP Officejet 8600 all-in-one would not pull from the optional second tray. There is a 10/22/14 driver update that says it is for OSSX 10.10, but does not fix the problem. After trying every single solution I could think of, including deleting all printers from my system, repairing permissions, installing the new driver, uninstalling and re-installing the second tray, among other things, nothing worked.
The problem appears to be that every time I print, it unselects the "Optional Paper Tray Input" setting from the OS settings. One work around is to go in and make sure that box is checked each time I print, which is a pain and only works about 80% of the time.
The printer is an office printer and Tray 1 is envelopes. While I could put regular paper in Tray 1, that would be unfair to the other people in the office who use the printer and would need to manually do an envelope each time.
I called HP support and they basically told me that it was a bug that was not currently fixed. They said they would e-mail me when a new updated driver is released (I'll be holding my breath for that). I'm posting this here hoping that admins notice it and get moving on that update so that I can get my printer back.