Why does an ajax form inside of an if statement submit twice if it is submitted after first failing the condition?

Why does an ajax form inside of an if statement submit twice if it is
submitted after first failing the condition?

References

Reference NO 1

http://stackoverflow.com/questions/15188074/why-does-an-ajax-form-inside-of-an-if-statement-submit-twice-if-it-is-submitted

Reference NO 2

http://stackoverflow.com/questions/14993047/why-does-my-jquery-ajax-form-submit-once-on-first-submit-twice-on-second-submit

Reference NO 3

http://www.faridhadi.com/submitting-a-form-without-reloading-the-page-using-jquery-and-ajax/

Reference NO 4

https://drupal.org/node/634616

Reference NO 5

http://tutorialzine.com/2009/09/fancy-contact-form/

Reference NO 6

http://www.yiiframework.com/forum/index.php/topic/37075-form-validation-with-ajaxsubmitbutton/

Reference NO 7

http://coding.smashingmagazine.com/2010/02/10/some-things-you-should-know-about-ajax/

Reference NO 8

http://bytes.com/topic/javascript/answers/872931-why-function-not-returning-false