Some RDP clients handle mouse pointer and touch differently. Some you have to toggle touch or mouse pointer. This may be the case. You could look into a new RDP client app if this is the case.
tested on one our tablets to day connecting using x2 rdp (android) and in order to get it to scroll you need to tap and hold until the circle appears and then you can scroll up and down with your finger on the list rather than the scroll bar.
That would be how the RDP client for Android is handling the behavior. You might try out other clients… but they may be similar or there may not be a better client out there right now.