Is this entry still in your database now? Clearly this condition should never happen - if zero-length values are valid for the syntax, then it should have been preserved in the (normalized) a_nvals. If not, then it should not have been in the a_vals in the first place.

No, it got deleted last night. But from the core I see:

at_syntax_oid = 0x100495d80 "1.3.6.1.4.1.1466.115.121.1.26"

IA5String, so empty string is valid. (And makes no logical sense in this situation, but that's for another day...)