Magnetized Dock?

[Invizzible]

I'm suddenly getting strange behavior on my Mac (running 10.3.9). If I open say, Safari, or Mail, and the window is filling up my entire monitor (vertically), I can't grab the top of the window and move the entire window down because after moving the window, when I let go of the mouse button, the window pops back up to the top of the screen (right up to the bottom of the menu bar). This only happens when my dock is positioned on the bottom of the screen. If the dock is hidden, or on either side, then this problem doesn't occur and I can move a full sized window anywhere I want. I've looked everywhere I can think of for a setting that will turn this obnoxious thing off, but haven't found one. Can anyone help?