Hrqls: You are of course right that statistics is required, but it is a) considerable work, and I don't want to bother if fencer seemingly is not interested anyway, and b) it is not always possible. One can't tell afterwards in which order the dice in different games have been rolled. So there is no way but recording during play. I once tried to create a tally sheet counting the equal and the different rolls when going from one BG game to the next, but I quickly lost track ... and see point a) above.
Ananju mentioned there is a way to reproduce the opponent's roll with higher probability than normal. This might be proven by analysing many old games, but if only few players know about this method and use it only in few situations, the statistical effect is very small and difficult to detect.
It seems we just have to accept the questionable dice rolling here. We may play here for fun, but for serious play one should go elsewhere.