Audiosnap grid drift

I've got a kick clip that I've used to pin the grid to in a song. Audiosnap has correctly identified all the hits and when I bring up the audiosnap tempo map it is correct throughout the duration of the clip. However when I select project follows clip (on the measure scale) it only follows for the first half of the song then the tempo grid starts to slide away from the audiosnap grid. 
 
What's going on? I followed the Audiosnap tutorials in Karl Rose's excellent SWA series. 

Ah Karl, your dulcet tones have been gracing my speakers a lot recently, really found the tutorials helpful.
 
I selected measure, it inserts the tempo changes but afterwards the grid lines on the project don't match up with the transients on the first beat of each measure, there's a small but noticeable delay, the grid lines are in front of the transients. It's weird because it pins the first half of the project fine. I ended up doing it by hand using shift-m and moving the now time through the project.