"Classes are not virtualizable" warning with resource-type non-virtual class declaration

On master, a basic manifest triggers a warning for virtualizable classes, which I think is incorrect:

test.pp:

class a { }

class { 'a': }

$ be puppet parser validate test.pp

Warning: Classes are not virtualizable at test.pp:2:1

Prior to PUP-1606 being merged into master, this didn't occur. This warning does not appear to occur on the stable branch with PUP-1606, only on master with PUP-1606, so may only affect Puppet 5.