Several days I've played, I have had issues with this bug increasing in frequency, to the point of making me want to just log off.
The issue stems from trying to move items between containers/inventory (UI windows), and having it stop being selected/picked, or will change to an item that you move the item over instead. It also included making it difficult to manually turn the camera via mouse.
I posted in Help about it, and it has helped to have changed the batteries in my mouse, but it was suggested to post about the drag-drop issue in forum anyhow, since several other players mentioned having the problem as well, in varying degrees.
If this is hard to understand, I'll try getting pictures to attempt to visually explain or to explain further.