if i understand you right, you clicked the zoom in icon and explicitly changed modes. and then on windows, if you clicked the DynamicCrop window, PI would automatically switch cursor modes back to DC, is that right?
i'd expect something like that to be the same across platforms, so maybe juan can comment on that.
anyway, i don't know if multitouch gestures need to be enabled in the OS but you should be able to zoom in and out with two-finger up and down swipes on the trackpad. and if you hold down the space bar you should be able to pan around with the trackpad (with one finger).
rob