OPLOT fired a missile!
The Oplot and T-90 can both fire ATGM's down their main gun barrels but this is the first time I've seen one actually do it. It caught me by surprise, I was just running some general tests and this Oplot and T-90 were on 'Fast' speed on roughly parallel courses when the Oplot let fly with this Kombat ATGM (circled)..
..and it hit the T-90 turret front, immobilising the tank. The T-90's gun was pointing at the Oplot. And although the T-90 was carrying AT-11 ATGM's, it chose to fire back with APFSDS a few seconds later and knocked out the Oplot.
Summary: I presume the Oplot crew fired the Kombat because it was a side shot and they decided a Kombat could easily penetrate, rather than waste an APFSDS round, but unluckily for them it hit the thick turret front instead of the side armour.
Or maybe because both tanks were on Fast speed, the Oplot crew thought they had more chance of a hit with a locked-on missile than with APFSDS, we don't really know what computations go in in their little pixellated brains.
PS- I suspect many of us players don't always notice when a tank fires an ATGM in the heat of combat because it sounds like an ordinary gunshot, (so do all other missiles in the game) and I can't find a sound mod to make them go whoosh..:)