In Virtual Wire mode, the Palo Alto Networks device can pass Cisco Link Aggregation Control Protocol traffic in vwire only when the links are not aggregated on the PAN-fw. In V-wire if the Links are aggregated then the firewall could forward the packets to the other ports in AE , that will cause the LACP to not come between peers.
Topology example
Switch 1 Configuration
Switch 2 Configuration
port-channel load-balance dst-ip
interface Port-channel5
switchport access vlan 10
switchport mode access
interface GigabitEthernet0/1
switchport access vlan 10
switchport mode access
channel-group 5 mode active
!
interface GigabitEthernet0/2
switchport access vlan 10
switchport mode access
channel-group 5 mode active
!
interface GigabitEthernet0/3
switchport access vlan 10
switchport mode access
!
port-channel load-balance dst-ip
interface Port-channel10
switchport access vlan 10
switchport mode access
!
interface GigabitEthernet0/13
switchport access vlan 10
switchport mode access
channel-group 10 mode active
!
interface GigabitEthernet0/14
switchport access vlan 10
switchport mode access
channel-group 10 mode active
!
interface GigabitEthernet0/15
switchport access vlan 10
switchport mode access
!
Firewall configuration
This is the expected behavior in 7.1.x and 8.0.x
More information on 802.3ad link aggregation can be found on wikipedia's Link aggregation page.