nested esxi, NIC issues

I have a nested esxi host with 2 port groups. VM Net and VM Test. The hosting ESXi has the same port groups, VM Net and VM Test. My problem is that VMs in the nested ESXi VM Test cannot ping VMs in the hosting ESXi VM Test port group (VM Net works). Do I need to do something special to make nested ESXi networking work? Some details:

All hosts are the free license. The ESXi host is 5.1. The nested host is 6.5 (same problem on 6.0). The ESXi host has 2 port groups, VM Net and VM Test. The ESXi VM has 2 NICs, one in VM Net and the other in VM Test. The nested ESXi has 2 port groups (VM Net and Test), defined to vswitches connected to the adaptors in VM Net and Test respectively.

VMs in VM Net in the nested ESXi can ping VMs in the outer ESXi VM Net. VMs in VM Test can't ping VMs in the outer ESXi VM Test. VMs in the nested VM Test can ping each other.

I've gone over the configuration but don't see any differences in the setup that works (VM Net) and the one that doesn't (VM Test). Any ideas?