NightProbe,
[ I edited this post, because my original posting was incorrect. ]
You can get this to work for the case where there is 4 digits in the year, and the years are sufficiently current. Use this for your transformation:
-dd/%Y-%m/
The reason I didn't support this mode is that this is considered an incomplete date. Since the code does not accept incomplete (ambiguous dates), it tries to parse the year as a mm-yy value. I noted this limitation here: Dynamic Renamer
In your case, the date September 2014 is being guessed as 9 for the month, 20 for the day, and 14 ==> 2014 for the year, so it will work for what I think you are doing.