Just thought I'd share a conversation I had with my local outboard engineer ( this guy is apprentice trained, now in his mid 50's so probably been there & done it engine wise)
He was stripping down a 120 Tohatsu attached to a 6.5 Humber dive rib, the club was reporting the boat would engage forward gear whilst it was just at idle all by itself
( look for it in the next episode of 'Most Haunted!)
Having been down all the usual avenues he discovered the cause to be of all things worn engine mounts, his guess being the extra wear allowing more vibration against a fixed throttle cable and 'click' off she goes!
He'd never come across this before but I thought it might be useful if anyone else has problems.