caching problem with MD3000i and Linux multipath

We have 2 Dell servers and a MD3000i SAN.

The configuration is the following:

                                          __________
host1 =----switch1=---=|SPA
               \ /       \ /              |
               X          x             |  MD3000i
               / \        / \             |
host2 =----switch2=---=|SPB
                                          |_________

Both hosts are Fedora 13. We use dm-multipath (multipathd). Qemu-kvm is the hypervisor.
The problem is that when host1 writes something to the SAN host 2 won't see it until the host reestablishes a connection to the LUN (i.e. log of the iscsi targets and log in again). So writing a file on the LUN by host1 is not visible by host2 which has also mounted that LUN.

The consequense of the cachingproblem is that when a VM migrates to the other host it will crash because the virtual disk is different for host 1 and 2. Migrating with Qemu-kvm succeeds when both hosts are just rebooted since both hosts see the same virtual disk (no caching yet).

Another problem that arises is the when the virtual machine is "forced off" the guest OS won't start again and gives a lot of disk errors.

Does anyone have a clue which component is caching? Is it the MD3000i itself? iSCSI-client (iscsiadm)? Multipathd? LVM?

Thanks advance!