I only get it occasionally slip out of 2nd into neutral cos I was too girly with the upshift, or was clutchless shifting again, and unlike Hondas, you really need the clutch for 1st to 2nd on mine but all the others, clutchless is fine ... on mine.
And the only real annoyance with the big vee is the space in the revs between 1st & 2nd, change any earlier than 6K in first and you're under 4K in 2nd which = no smiles at all. Big ratio step almost like the 5th to 6th
Grrr:-)
EDIT: PS: Any chance it's a simple case of the clutch not quite separating enough and just adjust the clutch lever setting thingy with the numbers on it .... something or other??