Is it intended to one spell negate other?
Creeping Cold dispel all niac's biting cold spells from mob - i found no word in known issues.
And same with two creeping colds from different druids. Greater Creeping Cold and Creeping Cold works fine together, but there's no way to two or more druids put CC on boss at same time, one "delete" other.
It pretty annoying when U're druid caster, and really got not too much other choises to nuke bosses, especially good like Creeping Cold spells.