I've noticed the same thing in a recent game, Xzanron. It doesn't happen all the time for me though. Most times I can still review the odds, but a couple times it's committed the attack without me releasing the button. I'm trying to recall if it occurred near water or not as I recently noticed unit targetting being a pain when there's a ship in the tile beneath. Do you have "stack attack" checked?
Llama,
If you "right-click and hold" the mouse button down and then drag the mouse around, as long as you don't release the rmouse you can check your combat odds against enemy units. If you like the odds, release over the enemy and your troops will move and attack. If you don't like the odds, you move the mouse back over your stack(or over the water, or off the screen) and release and no move will be committed. It has always worked that way in Civ IV.
