Fuse, fuze who the eff cares. I can't tell. All I know was that when I was trained on the 60mm mortar in the Irish army. We were told you could do that.
But I hate to think of the situation where it's needed.
But the big no no was to drop another mortar shell into the tube when the first one misfired. Just after we finished training, somebody did just that and blew themselves up.

As a result there was a moratorium on mortar firing and I never got to fire a live mortar.
We were not happy with those poor dead guys. Soldiers can be so brutal.