Windows cluster anti-affinity - what am I missing?

I'm attempting to set up anti-affinity rules in a two-node Windows 2012 cluster. I'm doing something like:

$value = New-Object System.Collections.Specialized.StringCollection;
$value.Add('ArbitraryString');
(get-clustergroup group1).AntiAffinityClassNames = $value;
(get-clustergroup group2).AntiAffinityClassNames = $value;

Before I initiate a failover, group1 and group2 are on different nodes. However, after I initiate a failover of group1, group2 doesn't move away from group1. What am I missing?

It should be noted that one of these groups is a SQL Availability Group (the other is not; I just don't want it to be hosted on the same node as the primary for the AG). So, failover of that group isn't initiated through cluster administrator, but rather through SQL Server. I don't think it's relevant, but just in case it is…