Machinbird,
its not how you imagine it.
I have flown both the B737NG and the A320.
On the 737, in order to select Heading, you need to push a button that is below the "round" Heading Select Knob to engage HDG mode and get out of LNAV. I doubt it is different on the B747. I have not flown the B747 but looking at the MCP it appears to be almost identical. On the 737NG you could not push the HDG knob, you could only twist/rotate it. To engage LNAV you need to press the LNAV button.
On the Airbus you need to pull the Heading Select Knob to engage HDG. You push it to engage Managed Nav.
In my opinion, you can not confuse the two methods of selecting Heading.