Coming up to a roundabout, there are two lanes, plus a cycle box at the front. There is also, for what it's worth, a subway under the roundabout which is bike-accessible, for people who choose to use that. Traffic lights at the junction, so plenty of time to get into the cycle box, which was empty.
I was in the left-hand lane, signalling left. In front of me there was one car, but with plenty of space to its left. Three cyclists were to the left of us, in a row so that the first one was ahead of me (beside the front car) and the last was level with me. When the light turned red I saw her stick her arm out, wave to the others, then wobble and grab her bike again. So I figured she wasn't steady. In retrospect it is possible she thought this was a signal.
When the lights turned green, the cyclist in front started to cycle out in front of the front car and to the right (the car was a bit slow off the mark). Car ziggles forward and cyclist stops. Then all three started trying to move right across in front of the cars. I'd started to move but stopped over the junction.
It was all slow so no chance of hitting anyone - though there was plenty of honking from people behind who couldn't see why we'd started then stopped - but is there any reason a cyclist would choose to turn right from the left-hand lane, rather than using the cycle box or cycling in the correct lane? 