jQuery: form not submitting with $("#id").submit(), but will submit with a 'submit' button?

Change button's "submit" name to something else. That causes the problem. See dennisjq's answer at: http://forum.jquery.com/topic/submiting-a-form-programmatically-not-working

See the jQuery submit() documentation:

Forms and their child elements should not use input names or ids that conflict with properties of a form, such as submit, length, or method. Name conflicts can cause confusing failures. For a complete list of rules and to check your markup for these problems, see DOMLint.

I use $("form")[0].submit()

here $("form") returns an array of DOM elements so by accessing the relevant index we can get the DOM object for the form element and execute the submit() function within that DOM element.

Draw back is if you have several form elements within one html page you have to have an idea about correct order of "form"s

http://api.jquery.com/submit/

The jQuery submit() event adds an event listener to happen when you submit the form. So your code is binding essentially nothing to the submit event. If you want that form to be submitted, you use old-school JavaScript document.formName.submit().

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I'm leaving my original answer above intact to point out where I was off. What I meant to say, is that if you have a function like this, it's confusing why you would post the values in an ajax portion and then use jQuery to submit the form. In this case, I would bind the event to the click of the button, and then return true if you want it to return, otherwise, return false, like so:

$('#submit').click( function() {
  // ajax logic to test for what you want
  if (ajaxtrue) { return confirm(whatever); } else { return true;}
});

If this function returns true, then it counts as successful click of the submit button and the normal browser behavior happens. Then you've also separated the logic from the markup in the form of an event handler.

Hopefully this makes more sense.