Official comment
WHAT WHAT WHAT mode are you using to analyse your tracks? If the song is electronic in nature with a perfectly consistent tempo, you should use NORMAL analysis. If it's got a live drummer (eg. rock, disco), it should be analysed with DYNAMIC mode. Using the wrong analysis or syncing one properly analysed track with an incorrectly analysed one will result in an incorrect or wavering playback tempo as the software tries to compensate and keep sync.