In Studio 17, you know when you are in Smart mode by looking at the drop down icon at the end of the timeline toolbar - see the screen shot..
In Smart mode in that version, if you drag a clip from the Library and drop it onto a multi track timeline, all the tracks will move out the way of the inserted track, but once it is there if you try to move it around you will loses sync (this was fixed in later versions). So in 17, you need to create gaps in the timelines in order to reposition clips once you have added material to other tracks
The behavior your describe is called magnetic snapping - it is truned on and off with the magnet icon on the timeline toolbar