This has happened to me twice now, and I'm sorry I haven't got a film of it. Since the second time, I have turned on auto-film, so I should get film the next time it happens.
Here's the bug: when shooting an enemy plane from very close range, the "splash damage" from the 37mm cannon can insta-kill the Yak. The two situations where I've had this happen I was crossing through an enemy plane, ie: it was passing from above my line of fire, through my line of fire, on its way down. I squeezed off a shot and hit the enemy plane from what has to have been 10-20 feet away, hit the enemy plane, and we both instantly exploded.
First off, the 37mm round would penetrate into the enemy plane's structure, so the round going off 15 feet in front of the Yak while inside the enemy plane would not be the same as the 37mm round going off in thin air 15ft in front of the Yak. The explosion, and shrapnel, from the explosion inside the enemy plane would be a lot less from the point of view of the firing aircraft. Secondly, this splash damage would not insta-kill the pilot. The pilot is protected, from this angle, by armor glass, as well as the engine block.
Secondly, this damage is being calculated wrongly. I have many times, with the Yak as well as with the 30mm guns of the 109 and the ME 262, got direct hits into the enemy engine block, and the result was just the enemy's engine stops instantly, but the pilot isn't killed, nor does the plane immediately break apart. How would direct into the engine block hits with the 37mm or 30mm cannon not insta-kill the plane so hit, but a hit into another plane 15 feet out in front of the firing plane insta-kills the firing plane?
I think this is a bug. If I can manage to duplicate this behavior on film, I'll submit that too.