[oast]

In the 'sitetemplates' directory add another .htaccess file with the one line

RemoveType .htm .html .shtml

That will undo what the AddType did in your root, in effect setting the extensions back to their defaults.

==Extra Note==
You could/should put it in any directories below root in which you have .htm(l) files to prevent the server wasting resources as it tries to parse static .htm(l) files.