I have the MF628Cw and I have the same problem. I would like to have the manual slot as the default. In other words, if I have inserted a sheet (99.9% of the time for me a 8 1/2 x 11) into the manual slot please use it. If no sheet in the slot, pull from the lower tray.
Even though I've checked and checked the settings, it will pull from the lower tray even though I have a sheet in the manual slot. My work around: I have to go into print settings and specify "multi-purpose tray" instead of "default" to get it to pull from the slot.
Any ideas?