Shawn,
I'm sure RVDT will correct me if I'm wrong, but making the assumption the EC-155 and EC-135 systems are essentially similar when in basic ATT mode (ignoring Upper Mode engagement) I think you are possibly misinterpreting the meaning of Auto Trim. The Auto Trim basically means the AP is operating in Attitude mode, and that Auto-trimming will take place to ensure continuous series actuator (SEMA) centralisation, and control movement to maintain Attitude datums - particularly noticeable with the heading holding (not HDG Hold.)
There are two basic modes of operation - Follow up trim, which ECF call 'Tactical Mode' and a conventional mode, which ECF call 'cruise mode.'
The follow up trim operates below 40 KIAS, and allows the pilot to push against the cyclic and the AP will re-datum to the new attitude. There is obviously hysteresis built into the transition, such that on departure the AP will have reverted to cruise mode BY 40 KIAS, and on deceleration the AP starts to transition back to 'Tac' mode at 40 KIAS and has fully reverted BY 30 KIAS, to give a seamless feel to the pilot. In 'Tac' mode it's a bit like the SFENA system found on some Bell 212s.
In 'tac' mode the AP respects heading hold at all times (if the pedal micro-switches are released) whereas in cruise mode it is roll dependant, and varies between heading hold and turn co-ordination. In cruise mode the cyclic behaves as with any other ATT system, when displaced.
The Cyclic and Yaw Auto Trim functions can be de-selected independantly using the APMS (Auto Pilot Mode Select) panel, which could be quite useful in the event of a trim runwaway - the pilot can retain the remaining AP functions whilst deselecting the relevant channel. (By comparison, if I have a yaw trim problem in the S-92 and deselect it, the whol AFCS goes into SAS mode and I have no coupled functions at all. In the 155, I could take out Yaw A.Trim and keep ALT, IAS and NAV coupling and just use my feet to keep trimmed in yaw. Anyway, don't get me started.....)
With the 155, the transition during the departure is programed to not only adopt cruise mode, but to alter the nose down attitude to that required for a Vy climb - so the pilot sets 10 degrees nose down in the hover, the AP trims to that datum, the aircraft accelerates and as it passes 40 KIAS the nose starts to rise and adopts an 80 KIAS climb attitude. I understand it's part of an intention ECF had for a fully automated Cat A take off. Still requires a bit of cyclic beep in roll, though, otherwise you end up in a climbing turn!
I sincerely hope that this is not 'duff gen' in relation to the 135, and should it prove so I will delete the relevant portions- the limited 135 info I have, though, (conversion notes from a large UK onshore operator) suggests the systems are near identical.