From a bug report, the weight of a non-cursed bag
of holding would be off by 1 when the weight of contents was a multiple
of 2 (for uncursed) or of 4 (for blessed), since the round off handling
added 1 when it shouldn't in those cases. Mainly noticeable when empty;
the extra 1 unit made it be twice as heavy as it should have been.
Probably never noticed in actual play. He has implemented a patch
which shows weights as part of an object's formatted description, making
this stand out. Supposedly the Vulture's Eye interface also added a
patch like that a farily long time ago; I wonder why nobody using it ever
noticed. (Maybe the weight was suppressed for bags of holding there?)