There are some bug on parseExact function where check literal return value is not checked producing as consequence that invalid dates are accepted.
You can see this in http://jsfiddle.net/OnaBai/LnaTq/1/
Where I show that a date as String that equals to 2012-09-26 and parsed with format HH:mm is recognized as Jan 01 1900 20:12:00
because the 2012 gets converted into 20 hours and 12 minutes.
As I mentioned above the bug is due to the fact that checkLiteral return value is not tested in parseExact function allowing the execution to continue skipping the ':' of the format string.
If you want me to send you fixed solution I have already implemented it. By the way, watch out that all but one checkLiteral should be checked for false.