Input text disappear after losing focus

I'm testing a website with heavy Ajax usage, right now we have more than 100 successful tests but now I'm running into this particular issue:

I have an input field with a hint value in it. The default value is something like "type e-mail here" and disappears when the field is focused. I can manage to achieve that the type(locator, value) method write the appropriate text in the field. But when the focus gets off the field to click the submit button, its value disappears and the post is done with an empty value.

I've tried firing onfocus and onblur events without success. Also typing the e-mail address character by character. Has anyone run into this same problem? Have you solved? Thanks!