When in dual monitor setup, the secondary display to the left from primary (has negative coordinates afaik), Rainlendar acts erratically. Window "on desktop" setting (need for Win+D shortcut). When dragging windows, they tend to blink rapidly and when they do, they have a "ghost window" elsewhere on the screen, which does the same movement as the window itself. If I stop dragging the window in a wrong moment, it may end up behind the screen edge. Restarting usually gets it where it should be.
Also there are some issues with docking/undocking which changes the monitor setup, but haven't had time to check what exactly goes wrong yet. Later.
Edit: tried with b48