Extra characters rendered in view that cannot be found! A possible bug in rendering engine?

I have a very strange error when rendering the index view
Rails is rendering the characters us at the bottom of the screen, below an index table, and I cannot find these characters in the view.
This part of the view looks like

us The part from id=content is yield in a layout file <%= yield %> When I delete the content of the view template, i.e the the **us** is still there When I delete <%= yield %> in the layout, the **us** disappears When I search for the **us** in the view code it is not found When I add my own extra characters in the bottom of the view template code, i.e after the **us** is displayed after these characters When I delete the layout the **us** is still there The only thing I can come up with is that us is generated by the yield function in some way, but that seems as a very strange explanation!

Anyone that has had this problem before?
Anyone that know how to find extra characters as us in the code ?
Could it be a bug in the rendering engine ?

Any advices would be great appreciated