Shy
Your 'N' had a faulty trim release system then. This would have been due to trim release power defect, trim release switch / wiring defect etc.

Blade
Yes, you were and are spot on. The only exeptionto the rule is if you carry out a rapid turn, climb or decent eg: 60 deg bank angle. Again (As expected) the trim system will not cope and here you may have to momentarily press the trim release switch on the cyclic to effectively resychronise the system.

However, normal flying (Rate 1 turns etc) you should be able to engage higher modes (HDG, ALT HOLD etc) and fly complete hands off without any problem at all.

No, it was de-modded by removing all the stab equipment to reduce the weight for police role equipment. We flew it for four years as a floppy stick-er. Our "loaner" aircraft had stick trim as per the original specification. It was interesting to fly, especially at night or in poor visibility.

Bladecrack
 

Having checked the manual, my comments refer to thre SFIM AP85 T31 as fitted to the 350s.

In older choppers such as the Hughey, the trim switch disengages the mag clutches of the force trim. This (as previously said) allows repositioning of the stick to a new "Neutral" position. The force trim really provided an artificial feel due to large springs, as with out the feel it was easily possible to over control the aircraft due to the powerful hydraulics.

With other airframes I dont know, as I havent worked on them.