The shamans and druids can give a long lasting buff "Spirit of the Enduring" with the Effect "Slot 1: Increase Current Hit Points by 1202 per tick". Shaman got a short duration Spell "Dissident Roar" which lasts 3 tics and has 2 Effects: Slot 1: Increase Current Hit Points by 7093 per tick Slot 5: Add Melee Proc: Dissident Roar Strike 1 with 400% Rate Mod I presume that all meeles like the damage-proc in Slot 5 and the additional regenerating actually residing in Slot 1. As the regenerating part of both are in the same Slot 1, at any cast of Dissident Roar, the Buff "Spirit of Enduring" is cancelled. Lately I am grouping regualry with a nec in the group. Specially the necromancer likes the regenerating of "Spirit of Enduring" as it counters nicely the HP loss caused by his lich-form. It would be nice, if for the HP-regenerating part of the "Dissident Roar" could be found a Slot different from Slot 1.
Last I knew, this was the intended behavior and is not a bug. There was a discussion in TBL beta when dissident came out as to getting this looked at, but it was either shot down or ignored. There were other discussions around the time Dicho came out as well. The necro should block Roar and therefore will not lose Enduring (it shouldn't matter during play ... I suspect he just cares about downtimes). While playing, Roar is always going to heal as much as Enduring over a minute (Roar's refresh time) so it really doesn't matter for anyone else not losing hps naturally over time.
It was the closest thing that druids had to an HoT so allowing shaman the ability to overwrite the buff for a few tycks of real HoT was a good way to snub one class while stroking the other.