It will try and place warp markers to what it thinks is the correct BPM, but most of the time Ableton gets it wrong. You can put a single warp marker at the beginning of the track, right-click on the marker, and select "Warp From Here (Straight)." This deletes every other warp marker, and should get you pretty close to the original tempo of the song. Then you can manually enter the tempo (say from 128.05 to 128 if it's a house track)!