Welcome to the near miss Victory club.
Wife and I are both members.
Some Victories do this. Though I have not heard it associated with a backfire. So yours could be something different. They may find a loose battery connection for instance.
There is a problem with some Victories that Ma Vic isn't talking about .
Some Victories are very sensitive to having the clutch pulled in too long during a shift. Mine stock seemed to fall in that category. Almost killed me last winter. It was real close. It's not stock anymore. That event prompted me to get off my wallet and start looking for a solution.
Some are sensitive to blipping the throttle to speed match the trans during a down shift. My wife's XR falls in that category stock so we added a pcv and a timing wheel to her's too in the hopes of solving that problem.
Avoid both of those behaviors if you have one of the bikes that have this defect, you'll probably live longer.
Both of our bikes seem to run much better and feel much more unlikely to stall after installing the PCV and the timing wheel. However since no one except Victory really has a grip on the problem it's a guess as to if we have really fixed it by adding these items.
My wife isn't about to start blipping the throttle on down shifts to test if the problem is fixed. As you found out these bikes tend to lock the rear wheel when they stall and she has no desire to go down to prove that the bike isn't really fixed. The several stalls she experienced were enough to convince her she didn't want to take a chance on it happening again. Now she just down shifts her Vic without speed matching and the bike no longer stalls and locks the rear wheel. That makes her happy
When she is on her HD's she switches to HD mode and shifts like a normal person without any fear of them stalling. That too makes her happy
When she's happy my life is better
Myself I'm not near as smart as my wife so I may try this winter to see if I have actually solved the stalling problem on mine. If not I have a Lloyd's Idle air valve I will add to see if that in addition to the other parts will actually solve the stalling during slow shifts problem with mine.
Anyway don't be surprised when the dealer says they can't duplicate the problem if your bike has these issues. They never can.
If they can't find anything concrete to point to, try not speed matching (blipping the throttle) and not holding the clutch for an extended period of time during a shift ( make sure if you start a shift you complete it in a timely manner) and see if the problem disappears.
If it does help, drop Victory a letter about it, tell them what you honestly think.
There is also a federal vehicle complaint form that can be found on line and filled out, don't neglect that. This is really a defect even if Victory would like it to be considered a feature. It's dangerous and needs to be addressed