Don't know of anything in the design that would cause this behavior, but I guess it is possible in later versions. (I doubt out) Do you have Security groups enabled? Since an instance can ping outbound and external systems can ping your instances, I doubt you have firewalls (iptables or the like) blocking this traffic.

I would systematically test pings while running tcpdump on both sides and see if that sheds any light. You can also run tcpdump from the hypervisor, if supported by your hypervisor, but you'll need to ensure you are looking at the right interface.

--Mike@Redapt

Update, I found the problem and was able to resolve it. I beleive this is by design as i had to add Ingress and Egress rules to the default security group. Basically i had to add the following rule:  

Protocol: ICMP, Start Port: -1, End Port: -1, CIDR: 0.0.0.0/0

This allows Ping between Instances.