Enum Comparison results in incorrect map behavior when using add assignment operator

In the attached test case you will see four methods which do the same three things. Each initializes a map, increments a value in the map, and then returns the map. The method called "works()" uses the add assignment operator to do this. The "buggy()" method is the same, but adds an enum comparison.

There is some interaction between the enum comparison and the += operator. The method "numericComparison()" is just like "buggy()," but performs an integer comparison. The "workaround()" method avoids the += operator. Both of these methods return a Map as expected.