I also had an issue with the Spectrum at Hemel.

I had many teething problems with the bot itself ...I used a normal Futaba 40Mhz on the Saturday ( burnt out a speedo and some reception issues plus cr*p driving ) and changed over to a Spekky on Sunday.

I powered up in the Arena ...moved away and the bot fired ..... settled ..and continued to fire intermitently throughout the fight.

Futher investigation showed something that I should really have noticed.. the switch ( Pico ) was very very close to ON with the stick centered ....so close in fact that it was indeed ON sometimes.
This was easily fixed by trimming away.

The fault.. if it can be called that... could have been extremely dangerous and I hope that I remember the fix if I ever have to borrow a transmitter.