Hard to tell with no code to look at.
Is your form in a dialog? What you are seeing is part of the URL
for a dialog page.
How are you submitting the form? What is the action that you used on
the <form>
element? Can you show your HTML? If your server code won't tolerate that,
you need to provide an action attribute.
e.g. <form action='http://example.com/xyz.php">
Did you just write
<form>
?