Bug - wrong win-rate displayed in tournament

I was astonished to find a bug with lichess. I would have thought it is quite matured, there wont be any bugs.

I have played in a tournament, won 6 games, lost 5, draw 2.
So I won more games than I lost. However, the win-rate is only 46%.
My last game was about 25 seconds before the tournament finished, so it is not the case that one win was not over when this bug (wrong calculation) happened.

What could cause this win-rate percentage calculation? Maybe if my opponent berserk me?
Or if my opponent is more than 400 points worse than me?

Here the tournament I have played in some minutes ago:
lichess.org/tournament/fhlnn5Tx

To be fair the rate at which you won was 46%. You won 6 games, you did not win 7 games (5 lost and 2 draws). 6/13 rounds to 46%.

I'm unsure if this is intended, but if you say win-rate is the rate at which you won games then draws are just games you didn't win.