Under the current system, if you get too small a share of a PK, the trophy
entry will be removed the next time you log on the character who participated
in the killing.
This is a planned feature rather than a bug, and there is no such thing as
V+ removing trophy entries (even if you beg for it we can't help you).
To conclude: If you're missing a trophy entry, you were most likely a lot
of people doing damage on the victim in question. If not, bug report it.