The tablesorter module could easily determine that "1 Apr 2012" is DMY order and "Apr 1 2012" is MDY order, but for some reason it doesn't. It just converts them to "1 4 2012" and "4 1 2012", respectively, and then assumes MDY or DMY order based on the global wiki configuration.
Gerrit changeset coming shortly.
Version: 1.19
Severity: major