I have had a near refusal of an engine to run on carb heat "on", but it was in extreme circumstances, on a a Harvard, P&W 1340 cubes, 650 odd bhp, OAT about 35deg, field 4000ft amsl.
Yes, I would imagine problems at a density altitude of 7000' and with 150 celcius in the carb throat. Use of the primer would probably weaken the mixture!
(I jest of course)
I have also heard of a case of an aircraft having engine cut-out on takeoff following carb icing on a long taxy out.
I'm not suprised at that. Even considering my meagre experience I have seen icing when taxing on numerous occasions.
Moral. Most of the time everthing is OK. Just now and then you get bitten.
I'm sure. I guess there should be a midicum of flexibility to deal with the exceptions (like the one above).