the string matching behavior when using a selector statement has changed sometime between versions 3.3.1 and 3.5.1 (future parser)
Strings matched whether they are capitalized or not. (e.g. Debian and debian)
Only lower case is matched (e.g. debian)
This breaks many existing puppet modules!
Many modules match facts like ::osfamily. They will fail because the capitalized fact no longer matches.
Some example code illustrating the problem is available at https://gist.github.com/fadenb/a785f40de0c6c7567928
If you need futher information please do not hesitate to contact me (IRC is probably the fastest way)