For the 1. issue (report an opened rollershutter because of an up command) please use autoupdate=“false”:
Rollershutter Shutter_GF_Living "Shutter" (GF_Living, Shutters) { knx="4/2/10, 4/2/11, 4/2/12", autoupdate="false" }
the effect is, the item will only be updated from commands or states from knx bus, but not from commands initiated by openHAB itself (UI or rules) Of course you still can update the state with <item>.postUpdate(state).
For the 2nd issue (Step after manual stop) I did not notice such behavior, so please show the complete definition (including rules) regarding your rollershutter.
Configuration with absolute position should be like
Rollershutter Shutter_GF_Living "Shutter" (GF_Living, Shutters) { knx="4/2/10, 4/2/11, 4/2/12+<4/2/13", autoupdate="false" }
where 4/2/13 would be the position read and 4/2/12 would be the position set GA, so openHAB would read the state at startup from 4/2/13 and would change the item state if receiving any messages at 4/2/13 or 4/2/12 but would never send a command to 4/2/13