Anyone ever figure this one out? I've got the same problem. When I print to my printer from another app, there is a specific paper size that shows up, as defined by the printer's driver. For some reason, in printer setup, this paper size isn't selectable from the list of defaults, and adding it manually still won't fix it.
It seems to print ONLY when the paper size is specifically set to what the driver wants, and Automator seems to totally ignore that.