Its being shutoff so what you suggest may in fact be occurring.
I also received a suggestion that I may want to "Close the spark plug gap a bit. Cold propane is a lot harder to fire across than starting fluid is."
Anyway, the owner says that they've always started them that way when cold or at least have for quite some time, until the stepper motor failure.
He's happy so all is good, just thought it odd and unsatisfactory in my mind.
I have several that do the same when they are "cold"
The impression I get is that air may be getting into the fuel system when it's shut down for a while. Thus, extended cranking or starting the engine with an alternate fuel (the starting fluid) is needed to pump the air out of the fuel line until fuel finally gets to the carburetor.
I agree with Skip along with the fact that after the unit sits for a while the gas vapor has evaporated and must be pulled from the flow reg. to the carb.
You mentioned that you had 12" WC the regulator could be turned up a little to around 14" this will give a little more pressure but I dont know if it would make that big of a difference