I have been using HP and Canon printers for 30 years. But with a recent purchase of a MF743Cdw, printing to the Multi-Purpose Tray (MPT) has been a mystery and prints to Drawer1 unexpectedly and inconsistently. Sometimes it goes to the MPT. Reviewing community support has been no help and organized in a bewildering way, frankly. Easy to click on the fat Kudos button, but I don't see many Kudos out there 
Mostly unanswered questiosn shggesting where else to turn for answers.
Computer is an HP tower PC w Window 7 Pro 64 bit and all other software and hardware work as expected.
First, upon driver installation, in Printing Preferences we set up the default in Paper Source to "Auto" under the Paper Source tab. Most documents go to the Letter-Portrait 20 lb paper in Drawer 1.
Then to print Letter-Portrait 20 lb sheet-fed checks, we load check stock in the MPT and on the printer UI respond and click the Letter-Portrait icon and select 20lb paper.
Then in check printing software, we select MPT as Paper Source, click Paper Source Info, click Retrieve Paper Source Info which shows Letter-Portrait paper 20 lbs, click Close, click OK, click Print and the checks unexpectedly go to Drawer 1.
The process is both overly-complicated and does not work as expected.
Even the status of paper "Loaded" is inaccurate if paper is removed from the MPT or Drawer1 and the Retrieve Paper Source Info button is clicked.
What is the workaround here?