ruby embedded code in HTML doesn't work properly

Ruby code embedded on erb templates is not rendered properly.

It seems as it doesn't detect the end of the ruby code (the %> token).

As an example, on <li<%= ' class="open"' if must_open %> id="menu_item_1">, "id='menu_item_1'>" is not rendered as HTML.

If I remove the second '%' and write <li<%= ' class="open"' if must_open > id="menu_item_1">, then "id='menu_item_1'>" is rendered as proper HTML.

I think it may have some issue with the '%' symbol?