Still, the frontal armor issue with the IS-2 doesn´t seem to be that uncommon. In that engagement a lone IS-2 escapes the crossfire of a King Tiger, Raketenwerfer and Schreck - sidehits on short range included.
http://www.youtube.com/watch?v=aiaIlJmrJ14&list=UUyUcNdOxXcVt3o9eZKdza9w#t=30m0s
I saw the replay and ALL SHOTS were frontal hits.
29:40 KT frontal . Pen.
29:47 KT frontal . Crew shock
30:07 KT frontal . Pen.
30:11 Rak frontal . Bounce
30:13 KT frontal . Miss/Bounce
30:19 KT frontal . Bounce
30:25 KT frontal . Bounce
30:27 Rak frontal . Bounce
KT:
Pen 240-200 Armor 425/225
Chance - 64%-53.3% / 100%-97.56%
IS2:
Pen 250-190 Armor 375/205
Chance - 58.82%-44.7% / 100%-84.4%
From 6 shots, 2 penetrated, 1 crit, 1 might have missed and the other 2 bounced. FOR those % it´s just slightly unlucky RNG.
Bonus: take a look at the IS2 shot at 30:20. You would expect that to be a frontal hit right? Take a better look.