I have the same problem with my 05 Gasgas 300!
When it is hot and I stop for a minute or 2 it starts first kick, leave in any longer it needs several kicks and the choke on. Not the end of the world but on a cold day when there is lots of queing it feels like I'm trying to start the bike more than actually riding it.
Started with looking at the obvious stuff, plug, plug connector and have ended up changing the stator and voltage regulator. Spoke to Kev at gasgas and he suggested changing the float height as this might be due to when the engine is hot the fuel in the bowl evaporates!
Other than the starting it runs really well.