The Smart tool defaults to the Comp tool in the bottom half of a clip, and it's the Comp tool that mutes other clips in other lanes in favor of the one you click. It will also split out sections of a clip that you swipe and make matching splits and mutes in parallel lanes.
To select a whole clip, you need to click in the top half of the clip. To drag-select part of a clip, you either need to increase the height of the take lanes so that a third 'hotspot" opens in the center of the clip where you get the Select tool. Or switch to the dedicated Select tool (default accelerator F6, or T or middle-click to get the Tools palette - a.k.a. HUD = heads up display).
EDIT: You got it before I posted, but maybe the above will still help.