repeatedly need to relink a clip to a media file when launching the project

So I've seen this happen many times over the last few years.  Not a big deal, but wonder if anyone understands the cause of the problem.  Usually happens in a complex project that's gone thru a number of "save as's". When I launch the project there's sometimes a clip that needs to be relinked.  I relink it and everything's fine but the next time I open the project the same clip needs to be relinked.  Just happened (and this seems to be happening everytime I open the project).  I'll try and go in to more detail the next time I launch the project to see if there's anything obvious in the file name or path...

Thanks as always.  Can't say how much help I've gotten here...