IndexSet isStrictSubsetOf bug?

Is this a bug in IndexSet? It seems like it should return true, but it returns false:

IndexSet([0,2]).isStrictSubset(of: IndexSet([0,1,2]))

From the documentation:

Returns a Boolean value that indicates whether this set is a strict subset of the given set.
Set A is a strict subset of another set B if every member of A is also a member of B and B contains at least one element that is not a member of A.

Using Xcode 8 beta 1.