SSL not working on 404 pages [1.6]

[flix]

Hi, 

I have SSL enabled on all pages on my store but if someone tries to view a 404 page, SSL isn't forced by default.

Anyone else encountered this? 

For example, if you typed

http://mysite.com/a-page-that-does-not-exist, the link stays exactly like that and doesn't 1) force SSL or 2) redirect to https://mysite.com/404 like you would expect (but page itself is the normal 404 page).

If viewing any other page, and trying a regular http connection like

http://mysite.com/a-page-that-does-exist it perform normally as you would expect, and redirects to https://mysite.com/a-page-that-does-exist

Only pages not found are affected, but it's a non-SSL vulnerability I would like to close.

I've regenerated htaccess, but this made no difference. SSL is of course enabled for everything in the back office. 

Any help appreciated!!