Why so high Ping Latencies in VE LTM ?

I'm testing a mixed cluster of one physical (LTM 1600) server and one VE running on Hyper-V.

Both are running 12.1.2 and I got them clustered okay and I can do a failover to the VE node, but I ran across a problem with that. Specifically, if I do a continuous ping to the self-IP of the VE node when it's passive, I get consistent and low response times whether it's WAN or LAN.

The moment I make VE the active node for any traffic group, the ping times start to vary all over the place. Even on the LAN, it goes from < 1ms to anywhere from 1 - 500 ms and might even timeout on a few of them. Same with WAN where I was getting a consistent 65ms response when standby, but all over the place when active.

Any thoughts? The host machine for VE has dual 10-core Xeons and I've setup the guest machine with 8GB of RAM and 8 cores. The other guests on it aren't using much CPU at all when I've done my testing.

When the VE goes active, I don't see CPU activity doing much... it gets a little higher and I see the connection count rise, but nothing out of the ordinary.

I have VMQ's disabled everywhere (on the physical NICs as well as the virtual NIC setting) so that wouldn't be the problem. Plus, it's just strange that it only happens when it goes active.

I should try pinging the floating IP as well but it's probably the same. I first noticed it when pinging a virtual IP of one of my vservers and saw the varied latency, so the floating IP is probably doing the same thing.

FYI, I was using just plain GARP at first but switched to MAC Masquerading to see if that helped, but no difference. Besides, that wouldn't/shouldn't affect ping times to the self-IP.

It really just seems like something in the network stack on the underlying Linux is having a hard time... it'd be great to find out if this is common, or just a few people?