MVC :: Strange Behavior On Form Submit?

i have a strange issue happening while submiting a form:i have this in my form:

<input type="radio" name="type" onclick="document.getElementById('Type').value='Publiser';" />Publisher <br />
<input type="radio" name="type" onclick="document.getElementById('Type').value='Advertiser';" />Advertiser
<%: Html.TextBoxFor(m => m.Type)%>

the javascript is working perfectly and changes the value of the textbox.the problem happens when i submit the form - what is extracteed by the model from the textbox is the string "on", and after the submit, it also changes the value of the textbox to "on".when i load the field with a value from the model, it goes ok, and does not change