I can confirm this "bug" (annoyance, more than anything) on a fresh install of CentOS 6.3. Trying to install the whole package set (5.5 version) (Percona Server, XtraBackup and percona-toolkit) have undesired lateral effects by default: It tries to delete (ana)cron - because it depends on Postfix, which depends on what 5.1 server provides and also creates a conflict between Percona-Server-shared-51 and Percona-Server-shared-55, as this bug reports.
I can also confirm that the workaround solves the dependency problem.
I can confirm this "bug" (annoyance, more than anything) on a fresh install of CentOS 6.3. Trying to install the whole package set (5.5 version) (Percona Server, XtraBackup and percona-toolkit) have undesired lateral effects by default: It tries to delete (ana)cron - because it depends on Postfix, which depends on what 5.1 server provides and also creates a conflict between Percona- Server- shared- 51 and Percona- Server- shared- 55, as this bug reports.
I can also confirm that the workaround solves the dependency problem.