ECLiPSe 6.x and singleton variables

ECLiPSe 6.x, recently released, features an improved compiler, which, among other goodies, improves detection of singleton variables:

Additional singleton warnings: The new compiler will detect additional cases of singleton variables, namely those that occur only once in a branch of a disjunction.

This may sound like a mandatory feature until you realize that most other Prolog compilers fail to detect such cases of singleton variables.