The worst bugs seem to be:
1. Some commissions can't be fulfilled even though their requirements seem to be met. E.g. I have one for a "gray fair catboy" and multiple gray fair catboys (including one with no other traits), and it won't satisfy it.
2. Sometimes hybrids get duplicated at creation; I once had my hubble filled with copies of the same catboy.
3. "even" hybrids don't seem to display correctly, and breeding with one seemed to cause a crash that required rollback.