LVM volume group goes online and filesystem is mounted when not all physical volumes active

I'm experiencing a strange situation on a couple of our RHEL5.9 systems.

Upon boot, something seems to be going wrong when detecting the LUNs. In spite of this, the volume groups that use the physical volumes that are on these LUNs still go active and subsequently the filesystem is mounted.

When the application (an Oracle database in this case) then tries to use the filesystem, the result is massive corruption and a rather extensive recovery time.

This leads me to two questions:
1) What could be preventing the system from registering all the LUNs on the system? and
2) What could be the reason these volume groups go online when not all physical volumes are available? Isn't that not supposed to happen?

Maurice