VNX can't see initiators from one host, but only from one switch!

We just purchased a new blade system (DELL FX2). Each blade is configured with two fiber HBAs that are connected to two new downstream fiber switches. Each downstream switch has an ISL connection to a switch connected to the VNX.

Each blade's HBAs  show up on the appropriate switch. Everything looks great.

I zone the first blade, and all is well. All four paths show up in the 'initiator' screen in Unisphere. The host agent is checking in with the hostname. I can create a storage group and present LUNS.

Terrific!

I zone the second. Again, it's all good.

Then I get to the third, and for some reason,  switch's 1's paths do NOT show up! Switch 0's paths are fine. 

I double checked the zones. Deleted them. Re-added them. Disabled/Enabled the switch.

I checked for the zones and aliases on the connected upstream switch. Everything looks great.

I restarted the host agent, although I'm pretty sure the initiators should show up anyway.

I can't understand why these aren't showing up

Any idea of what I should try next?