Copter climbes in AltHold

The THR_MID value is set perfectly for stabilisedmode. But in AltHold my copter climbes gentaly if the throttle stick is in the mid-position. The missionplanner shows, that my throttle is trimmed right ( mid1500 min1100 max 1900)

Which value is set wrong? (raising the deadzone is not a good solution, because I dont want to loose 1/3 of my throttlestick range)
(I think that I search a value to trim the throttle-input for AltHoldMode)

Thanks for your help!

Please provide dataflash logs to help troubleshoot your issue.

Unfortunately Mission Planner always crashes, when downloading LogFiles :-/ The copter holdes his altitude when I trim the throttle on my remote -20% while hovering in AltHold. In Stableised it hovers pretty good at 0%trim at the remote.