Yeah, sounds like they’re just dice that don’t follow normal convention, then.
For the record, I prefer Chessex dice; their d20s do have opposite sides that add up properly (though that’s not why I like them 
).
Speaking of dice not following conventions, I have a die that probably came from a set of Pound o’ Dice, but looks different from the rest in general - a color not found in the rest of them, no speckling, different finish. But the really odd thing about this die is that the base of half the numbers point toward the peak, not the base, of the triangle. I’ve never seen that before, and it was almost disorienting when I first realized it. I’ve done the chi-squared test, and it passed with no problem. I’ve floated it in salt water, and it does seem to be lighter on one side, but not decidedly so such that it always rolls back around to show the same number on top.
Generally, it’s been behaving with the normal ups and downs, but for two weeks in a row it was throwing 19’s and 20’s at a prodigious rate. We were playing HackMaster, where a natural 20, and even a natural 19 is a much bigger deal than in D&D. I tore through some orcs, and my defenses scored me free attacks. Streaking happens with any random system, but damn.