Number keys no longer change opacity in Brush tool.

I always used the number keys to set opacity in brush tool. Suddenly it now affects flow, not opacity. At the same time this functionality changed I started having to click on a mask for the [ ] keys to change brush size. I used to be able to change size without selecting the mask. Did I inadvertently change some setting? I am using CS5 12.0 x 64 on Mac in 10.6.8. Thanks !!!

Are you pressing Shift when you type the numbers? Because doing that changes the flow

Press Alt+Shift and then try again to see if the problem persist.