The filler cap on mine has always behaved itself until a couple of weeks ago. I have now had about 3 occasions when it won't open at the first attempt. Obviously this wasn't modded during the 12500 service.
Anyway today I was in the garage sorting out the track bike and found a couple of small springs

got the car key and this is the result
works a treat, cap springs open with gusto now

, the spring is just the right dai the fit snuggly onto the little rubber stop.