Audio moving slightly after reopening a project

This is a problem with Audition and also Premiere Pro.

So I've had this problem for many years using premiere pro being that if you sync two audio clips with as much accuracy as you can using the "show audio time units" the audio will always go out of sync slightly after reponing the poject. (It sounds out of sync and you can clearly see the clips aren't lined up together with the waveforms matching where they were left).

Now I've always put up with this and just resorted to moving it back but it is extreemly anoying when you've spent a good while making sure two clips are perfectly synced and then have to do it again.

The thing that's really anoying is audition suffers from this problem too and I thought with premiere pro focusing on video I can put up with it, but why is Autidion (a specialist audio program) suffering from the same problem? 

If there is some way of fixing this please let me know but it seems that these programs simply lack the ability to record accurately where a audio track was placed in a project.