Self-extracting crank bolts

i have just tied to take off some strongshite cranks with self-extracting bolts, and BOTH of the black washer things have shat themselves, ruining the thread on the ds crank.
what the fuck is going on?

supremely fucking cunted off.

Don't know about the modern ones, but I'm pretty sure older Stronglight cranks have a different size thread for the crankbolt covers/extractor, this might be the problem, though if they were smaller you shouldn't have been able to get the caps screwed in. If they're larger (the threads on the crank) maybe they're close enough that you could screw the caps in, but sufficiently different that once you put pressure on the caps by trying to extract the bolts that they stripped the thread instead of biting enough to pull the crank off. Hope that makes sense, but yeah that sucks :)