When you mousedown on a slide bar (like the one used to increase % taxes spent on research), if your mouse goes above or below the actual bar while the mouse is still down, the slider stops moving. Normally this only happens if the mouse gets about 3 bar's width away from the slider, but in the game there is no room for your mouse to go above or below.
Also, this might be a feature rather than a bug, but you can't scroll down+right on the main screen (maybe to keep people from scrolling when they hit next turn).
