Yes -- I also see these type of V6 addresses. The response packets certainly wont go anywhere useful! It appears that I get about 20 of these per day.
Most of them are the EUI64 form (i.e. they are generated from the MAC address). However, the mac addresses are not clumped (so it seems unlikely that they are all from a single poor client implementation).
This is a chunk of mine from the last couple of days:
Oh -- I'm running entirely custom NTP server code, so it is very unlikely to be a server side implementation bug.