I'm found this problem too T.T
I can't say for certain, but I watched someone intentionally trying to reproduce this, and it seems like sometimes if you hold the column early and let go, the combo will keep rising and only register a 50.Rene was correct.
So you wouldn't normally get 50s for those hits? What happens if you run that replay on an older version of osu? If there really is a problem, I'd expect replays to give a different score now than before.I ended up making an new thread because the problem still exists t/351252
If you can find a replay that does demonstrate this, please post it here.