When? Under what circumstances?

When driving in second i.e. around corner before upshifting to third. Have my hand on the gearshift prior to upshifting and must accidently push it slightly and easily pops out of gear.

In 6,000 miles, mine has popped out of gear 2 or 3 times. And each time it was just because I didn't push it all the way in to start with. So it was my fault. Maybe that's what's happening to you?

Hope it's that....if not...

Hopefully, it is because of not fully engaging the gear. If not, I had a similar problem with other cars in the past where the car makes a loud noise as it pops out of gear.

Ended up being a gearbox problem.

I would just keep an eye out and be a little mindful of shifting for a while. If it happens again....off to the dealer.

Keeping my fingers crossed for you.

I've had this happen to me two or three. On all occasions it was during a hard left hand turn, that I upshifted during the turn.

In both cases, as I've powered out of the corner, it's popped out of second and "BANG" revs go up.

Second is a tad nochy, if you don't pull all the way back it tends to catch on the first notch.

I'm now shifting a bit more "spirited" and haven't seen this for months.

It occurs to me that while I've had it pop out of gear, this has NOT happened since I got my Rob Knob.