[ROM] Weak Bloodline Sim is not a proper spellcaster but can't become one

I figured it was intentional. I had a spellcaster-vampire couple with the spellcaster having an ancient bloodline trait. All four of his children had ancient bloodline (3 of the 4 were vampires). It makes sense that it would get passed down (at least to me, idk). If a sim with a bloodline marries a sim with no bloodline and is not a spellcaster (and you continue doing this for generations), the bloodline weakens (since you aren't getting that spellcaster blood mixed in). It could be a bug, but I always thought it was intentional.