as workaround i can create the hash via NSMutableDictionary.dictionary or in my case :

temp = YAML::load( NSString.alloc.initWithData( fileWrapper.regularFileContents, encoding:NSString.defaultCStringEncoding))

@data = NSMutableDictionary.dictionary

@data.setDictionary(temp)

is a bug or a behaviour that i do not understand?

Ciao