So, if you look at the stats here:
You see that on D2 for Heretics, flex0r played the T half and Kyojin played the CT half.
flex0r's T stats are 7-12 -5 66.5 46.7% with 0.66 rating. his CT stats are 0-0 0 0.0 100% with 0.98 rating. Overall his rating is 0.98.
Same thing happens for Kyojin. He has 1.16 rating for not playing at all on the T side.
It's also happened in T1, like this match between Na'Vi and Heroic in EPL 12, where electronic had technical issues on overpass and b1t stood in for a few rounds: hltv.org/matches/2343672/natus-vincere-v..
He has 1.14 rating on t side for not playing.
Another instance: hltv.org/matches/2341914/navi-junior-vs-..
Aunkere played Vertigo, CT side of Inferno and all but one round on T side of Inferno. Monesy has 1.00 rating for the CT side he didn't play, and 85.7% KAST for the T-side where he played one round and died it in.
Not a very big issue, but these things happen.