Any detail here? Did you leave the scene of the crab? If you leave the crab before he is done listening, you will keep them, but if you stay there, they should be taken back. I just went through a dialog with one, and the crab took his crabpod headphones back as expected.
I was given the headphones and got a little window telling me all about them and that no vendor would buy them. Then they went into my inventory. I now have two pair.
You're not supposed to keep them? He kept giving a new pair to me when I dumped them so I decided to keep a pair around. They can't be sold, but you can donate them! :P (you might win a ticket)
I think I must have been moving when he kept giving me new ones, will try staying still next time.
problem might be that I still had headphones from when it was broken and he felt like he had to give me back "my" headphones... I try dropping them then hunt down the crab.
I too own a pair of headphones (and I don't think I left the scene of the crab). Subsequent crabs only have given me a pair and taken them back when they are done listening (not sure why I need headphones so a crab can listen to my musicblock anyway).
You can't actually 'give' them back, the crab takes them when done listening to the musicblock. If anyone has them now, it's ok! It's actually not a problem to have a pair, or more even. You can actually drop them on the ground and when the crab is done, they won't be taken back at that point. Collect 'em! You won't get a trophy or a badge, but the crab won't hunt you down and pinch you either. :)
Ugh, and now we have the issue of headphones littering the world...people are dumping them out of their bags everywhere...at least let folks donate them or do something other than drop them everywhere.