Hi, I haven't heard of that particular issue before. When you are in the trim setup, it shows the stick input that it's reading. So the jumping you describe is the same that's causing the random input when flying too.
If you aren't experiencing that erratic input when flying for real then I guess there is nothing wrong with the transmitter. Might have something to do with the USB dongle (or USB drivers) perhaps.
I would suggest to try another dongle if possible, or, to try the Smartpropoplus method described in the manual and see if that helps.