Why do some hands that lose at showdown not show up in the HH?

[VarlosZ]

Just what the title says. I've noticed that on PokerStars, some hands that lose a showdown aren't listed in the hand history -- instead, it just says that the player mucked. It's generally in big pots, but other than that I can see no rhyme or reason to it. Anyone know the answer? Thanks.

[VarlosZ]

Bump. No one knows?

[soah]

were you dealt in?