www-apps/bugzilla-2.22.1 currently RDEPENDs on <=dev-perl/DBD-mysql-2.9007
because DBD::mysql 3.0003 to 3.0006 are broken. 2.9007 is currently marked
stable.
According to the software matrix in the Bugzilla FAQ (cf. URL specified above)
DBD::mysql versions >= 3.0007 are working fine with Bugzilla (which I can
confirm for 3.0008).
Some packages depend on newer DBD::mysql versions, though (e. g.
dev-perl/Template-Toolkit-2.15-r1), which causes conflicts, of course.
Therefore, I suggest to either change www-apps/bugzilla-2.22.1's RDEPEND to
something like
mysql? ( >=virtual/mysql-4.0 >=dev-perl/DBD-mysql-3.0007 )
which shouldn't be a problem as 2.22.1 is marked unstable itself or stabilize
>=dev-perl/DBD-mysql-3.0007.