I use UniversalMouse for scrolling, and I happen to have my middle mouse button mapped both to double-click and universal scroll. The scrolling doesn't work under R5's ShowImage for some reason, but to my delight, under Haiku's it does! However, it also selects a filled-in area the colour of whatever pixel was under the mouse when you start scrolling. On click, you can see it start to select, then scrolling is fine (it doesn't follow around/actually select anything yet), then when you let go of the middle button, it starts following the mouse, filling in solid. As the mouse moves, it flickers between solid and transparent, but when you're not moving, it's solid black or white or whatever was under the mouse when you started. Clicking and right-clicking won't disable it--at this point I have to press escape to get it to go away.
