They changed it in a patch, now "Zombie" state lose all his buffs and debuffs.
i Could not find the patch, i looked here but the last patch listed is from shyv (2011-10-31)
here a post that has similar question
What happen now is only the increase speed per time from his pasive. but Ghost instantly vanish from the bar.
PS: I don't know if this is a bug or not (because i could not find the patch), but it is how works now (2012-02-26) at least.