Multipath LUNs (paths) do not show up, or show up very late on RHEL 5.6

Issue

• After update server from RHEL 5.5 to 5.6 I have problem - periodically (after reboot) partitions from array (Hitachi AMS2500) do not come to server, I can't see them from fdisk and from multipath -ll.
  When my server work on RHEL 5.5 all partitions come correctly.

Setup

• BladeCenter HS22 blade with
• two QLogic 2532 (or 2572) fibre channel HBAs
  • 24:00.0 Fibre Channel: QLogic Corp. ISP2532-based 8Gb Fibre Channel to PCI Express HBA (rev 02)
    24:00.1 Fibre Channel: QLogic Corp. ISP2532-based 8Gb Fibre Channel to PCI Express HBA (rev 02)
• Brocade 5470 Switch Module, aka Brocade 8GbSAN Switch Module for IBM BladeCenter