When I have my bike running with the sidestand down and I sit on it and rock it to the left quite heavily, the bike cuts out.
This only happens when the side stand is down.
Anyone know why this is happening? 
Coz you have , like many other bike’s, a cut out switch attached to the side stand - stops you trying to drive off with it down!
Lose some weight and hey presto no problem
You say it only happens with the side stand down, but how far have you leant it over, and rocked it, without the stand down? It could be your tipover switch kicking in.
Call me crazy, but why do you want to rock it when its down?
When you kick your sidestand out it should cut the engine immediately if you have a sidestand cut out switch. It should not be running at all with the stand down…must be faulty.
Only when it is in gear. But it could be a faulty side stand switch. Or a dirty switch - try soaking it with WD40.
Yeah…Think you’re right mate…I noticed this only started happening after a mechanic checked the switch with a multimeter to see whether it was faulty when the bike wouldn’t start.
The multimeter said the switch was fine and the starting problem was traced back to the faulty Power Commander.
Could he have wired the switch back wrongly?
I don’t know…I’ll have a look when it’s not fooking raining (so never then).
its a yamaha 
could it be cos you binned it, which tends to do bad thinks to the wires and you’ll have an intermittent connection somewhere.
Thank god for that…I’d hate to be riding on one of those Shítezukis 
Nah…Like I said…It only started happening after the guy checked the switch.