IE ignores jQuery Validation

[EVENNAJAL]

Here's an example: http://jsfiddle.net/7g8GD/1/Once you have entered an invalid input and hit enter it returns 'Please enter your email address' as it should however if you hit enter again without changing the input the validation is ignored and the form continues as if the input was valid.What is the problem here?(when I use this on my server the problem only occurs in IE9 and not in Chrome, but in jsFiddle it happens in both)