With my own buff "Horn des Winters" the condition works fine.

In a group with another DK that cast "Horn des Winters" the condition fails.
My idea is, that the check checks only OWN buffs correct.

"Stärke der Erde" is a similar Buff from shaman (Earth Totem)

The reason musst be another one. at the next run all was fine .... I have to investigate...