Most recent JoomSEF for Joomla 1.7 has a small issue:
I have Joomla setting "Adds Suffix to URL" enabled and JoomSEF setting "File suffix" is '.html'

That is fine for components with SEF extension, but components who use native router rely on Joomla setting, so if "File suffix" is '.html' - "Adds Suffix to URL" should be also enabled, so the component knows how the links look like.

And this results in duplicate prefix - all URLs built via native router are like /forum.html.html

I think that JoomSEF shouldn't add its prefix to the URLs build via native router, so they can use Joomla setting as usual.

Please advice your thoughts.

Hello,

Thank you for your report, we'll look into this issue.

I also see these errors:

Notice: Undefined index: * in \components\com_sef\joomsef.php on line 1278
Notice: Trying to get property of non-object in \components\com_sef\joomsef.php on line 1278

Problems should be fixed in next JoomSEF version.