Capricious; unreliable (6)
I believe the answer is:
fickle
This clue is a double definition.
'capricious' is the first definition.
(I've seen this before)
'unreliable' is the second definition.
(I've seen this before)
(Other definitions for fickle that I've seen before include "Unreliable" , "Erratic, unpredictable" , "Inconstant, changeable" , "Often changing, not constant or loyal" , "Prone to shifting loyalties" .)