crazy dock

[don hinkle]

I've set the dock so that it hides or reappears when I press Cmd+Opt+D. 
That's cool.
HOWEVER, now the Dock persists in rising out of nowhere if I drop the 
cursor to the bottom of the screen. Sometimes I'm simply trying to reach 
something else down there and don't want the Dock to rise up--like a cat 
when you hold a hand over its back and it rises up to get petted.
I just checked the Dock System Preferences and Automatically Hide and 
Show the Dock has been Re-Checked after I deliberately Unchecked it.

What's going on? Why can't I make that order stick?