Hello!
Your package lxpanel-plugin-topmenu has a Build-Depend on lxpanel,
and since 0.8.2-1 it has lxpanel-dev package splitted out so I would
suggest to change that dependency to lxpanel-dev instead (or may be to
lxpanel-dev | lxpanel (<< 0.8.2-1) if you are going to backport it).
With best regards,
Andriy.