Thanks for all the responses, I'm at ~200 miles now and it's still occuring, possibly more.
I've adjusted shifting a bit but it was no help, I'm gonna try releasing the clutch while I'm still holding the shifter up and see if that help. I've been riding with steel tips to and from work so I think I've been putting plenty of force into the shift.
I guess I'll just keep trying and see what happens after more time.