Butler return wrong defects given a dataId

I'm taking data with N2 and R2 at lam and when I want to reduce N2 data, I'm first getting the defects from the butler, but I'm being told there are two matches :

RuntimeError: No unique lookup for {'taiObs', 'ccd'} from DataId(initialdata={'spectrograph': 2, 'arm': 'n', 'visit': 48702}, tag=set()): 2 matches

When I take an exposure on N2 only, I have one match.
But if we you play actually around and change arm and|or spectrograph in dataId, you get always the same defects.
It's like the butler is only matching on visit