I only spotted mine because it was the day after I fitted the Optimate and it had never done it before.
When I looked at the battery connections they seemed fine and tight, but wiggling the reg/rec underneath the tray caused sparks on the earth, so it obviously wasn't tight enough.
I thought this may be the case as I had an RGV250 that showed similar problems and I tracked that down to a bad earth too - one of the connectors was exposed to the elements under the seat. Replacing it and making sure it was nicely sealed cured it.
I'm sure it must be something to do with the vibrations of the bike that simply shakes things loose... that and throwing it down the road
