[CentOS] CD #1 & 4 flip-flop

[C.. Scott Heisler]

Does anyone know why the install CD set request the 1st CD during the loading of files from the 4th cd and then goes back to completing the setup on the 4th cd?
 
This started with the 4.2 version I believe (at least that's when I first noticed it) and I thought it was strange.  Now the 4.3 set does the same thing and I was wondering why.
 
Thanks.
Scott