I've got record shifters that are one year old. The last few rides, its felt like I periodically get an unintended double shift when shifting up the cassette toward the spokes. It almost feels like there is a missing tooth in the ratchet or something like that. Usually, there is a very distinct click for upshift on the cassette but every once in a while it jumps up 2 cogs. Any theories? I don't think it is the spring wearing out because all the other shifts are very distinct and not sloppy like when the spring starts to wear.