URL Scheme on media attachments is incorrectly set to https when administration performed over SSL

[khlo]

My site is set up as follows:

• Administration is performed at ​https://example.com/wp-admin. This uses a self-signed SSL certificate to protect against eavesdropping (e.g. on public wi-fi).
• The front-end is accessed through ​http://example.com.
• Our WordPress siteurl is set to ​http://example.com.
• We use define('FORCE_SSL_ADMIN', true); in wp-config.php to enforce SSL on the admin (but not on the front-end).

In WordPress 4.2, changeset [31614] was introduced to fix ticket #15928.

Unfortunately, this has broken images on our website. As administration is being performed over SSL, wp_get_attachment_url() returns an image with the ​https:// URL schema. This is then saved in the post. When readers access the post through our http front-end, images will not load as the img src attribute uses https (not available due to the self-signed certificate).

Expected behaviour: wp_get_attachment_url() should use the same URL schema as siteurl (i.e. it should use the http schema as we've specifically set this in our siteurl).

[boonebgorges]

Thanks for the report, khlo. We're tracking this issue at #32112. See especially https://core.trac.wordpress.org/ticket/32112#comment:14 and later.