I use the A320NX and i have regoniced that the thrust goes a bit up by it self, after setting up Flaps 1. I think that isnt real. But when i set the thrust again to idel it is all ok again. And also i have the issue when i set thrust the engines will for a short time go over the setted thrust by me.
And these are going shortly back to the setted thrust by me. And also sometimes at Takeoff the thrust goes by it self to idel until i set the Toga speed again. I use the newest Development Version of the A320nx.
This sounds like something missconfigured with your keyboard / button settings. Check if some of your buttons are mapped to the wrong action. Also check the sensitivity seetings of your controler and set a according deadzone.
If you use the experimental version with custom flybywire, also be sure you configured your thottler controler correctly (see instructions on our gitbhub page). You can also try the developer version first (same as the experimental, but without our custom flybywire).