mixing repositoies

[Stuart]

"Tom Horsley" wrote:
> > I have seen lots of admonitions about the dangers
> > of mixing packages from, for example, livna and
> > dries.  But I have not seen any clear technical 
> > descriptions of exactly *what* (with examples) the 
> > problem is!
> 
> You download mplayer from livna, all is working. Then
> you add freshrpms to get something from there that
> livna doesn't have, and it starts updating your
> mplayer libraries. Pretty soon nothing is from any
> consistent source and your system is a mess.

I guess what I don't understand (taking your 
example) is:
1) why should a package from freshrpms update the
mplayer libs if I already have current versions
installed?  
2) Even if it does (because the release number in
mplayer-version-release is higher), why will those 
versions break the livna mplayer?
I.e, I am having trouble with the meaning of your
word "consistent".