Drupal url which contans "http://" does not work, shows 404

Question

I have a Drigg site. (Based on Drupal) which has been working well, but suddenly it stopped working for one case. As this is a Digg clone, the site has a SUBMIT page (which contains url/title/description forms). This submit page works like this

http://example.com/submit?url=http://etc.com&title=blabla 

which fills url and title forms.

but suddenly it stopped working when the url has "http://"

But it works perfectly well for

> http://example.com/submit?url=etc.com&title=blabla

It shows the page, prepopulated/fills the forms, but when i add http:// it shows "Page not found" I didn't change anything ,it used to work a few days ago.

Why this is happening? How can i change this?