I've had that one too, it does make you jump!
I had it just following steady traffic and infront of me was a motor bike, but he was sort of hugging the central dashed white line. Then as traffic infront of us was slowing he quickly moved into the middle of the lane. Wasn't really close to him but I'm thinking perhaps the radar didn't pick him up properly or something and then suddenly heres there in the middle lane, maybe it thought someone had just cut infront of me and thats why it set it off.
Made me jump though, didn't know OK could clear it so thanks for that tip, I just had to drive on and wait for it to manually disappear. It didn't do any braking for me though as I was literally about to brake myself as it came on, but nothing other than gentle braking though.