[CentOS] Yum and case-sensitivity

Hi List,

On one of our servers (CentOS 4 32 bit), we have the dag repo enabled.  
Yesterday morning during a yum update, yum replaced the CentOS package  
"perl-DBD-MySQL" with one from dag, "perl-DBD-mysql".

For whatever reason, the two packages differ, in that only one of them  
(the CentOS built one) includes:
	/usr/lib/perl5/vendor_perl/5.8.5/i386-linux-thread-multi/Mysql.pm
	/usr/lib/perl5/vendor_perl/5.8.5/i386-linux-thread-multi/Mysql/ 
Statement.pm

I've excluded the dag version in our yum.conf so it won't re-apply it  
and break perl code that has "use Mysql;", but I'm confused as to why  
yum saw fit to replace the package, and, why it did so yesterday.  
(This box has not had any packages added or removed, outside the  
standard 'yum update', for many months; and the only repo other than  
CentOS-managed ones it he dag one.)

Bug? Expected behavior?