The first issue is that using a custom paper size (12x18 stored in the printer's "Custom size" parameter) in Tray 1 prevents the printer from using Tray 1 in cassette mode, i.e. to treat it like any other tray. If I load 11x17 into Tray 1, and set the paper size to "11x17", it will pull from there if I send it an 11x17 page and tell it to Automatically Select the paper source. However, if I set the size to "Custom" on the printer, then set the Custom size to 11x17, the printer will ask me to load 11x17 into Tray 3, which is where I normally keep it. This shows me there is an issue using custom paper sizes with cassette mode for Tray 1.
