[b28] Limmirs Amulet of Moon creation bugged?

[Willi]

Hi,

I was creating an Amulet of Moon with diamond(+5 all stats) and ruby(+4 all stats).
Result was +10 Defense and +5 all stats ... (tried it 2 times)

with ruby+onyx I got +12 to all stats
with diamond + onyx it was +13 to all stats

I tried it again with diamond+ruby -> +14 to all stats

Is it supposed to be random?