form_open_multipart doesn't use HTTPS

I spent quite a lot of time debugging tonigh, since my .htaccess kept redirecting after a file upload.

After a while, I realized that form_open_multipart() doesn't detect that the client loaded the page with https.
It doesn't seem to be an option to enable HTTPS on this either, so for now, I'll have to make the input manually.

Anyhow, wouldn't it make sense for the function to detect wheter or not the client is using SSL and apply that to the url of the form?