You don't have to repurchase them. Once you own them, you own them. You just have to reinstall them at a ripper doc.
That being said, I have the same bug too. Anytime I sell, disassemble, or generally do anything with grenades, I lose my cyberarms. Which means I have to constantly take a trip to a ripperdoc to reinstall because grenades have weight and I gotta offload them periodically.
If it helps, this bug occurred after helping Kerry blow up the van when he gave me a bunch of grenades during the "Rebel! Rebel!" mission. Didn't happen before that event.