I know it's 6 year ago...
I just stumbled across the same behavior and was able to solve it starting the page as follows:
<%@page language="abap"%>
<%@extension name="htmlb" prefix="htmlb"%>
<head>
<base target="_self">
</head>
<htmlb:content ....
Probably it does help someone else, as it is most probably a bit late to help you.
Best regards,
Frank