WP_Query orderby broken for menu_order when posts_per_page is set

[dan.rossiter]

Passing the following arguments to WP_Query results in a seemingly arbitrary ordering. Definitely not the menu order.

[posts_per_page] => 16,
[offset] => 0,
[orderby] => menu_order,
[order] => ASC,
[post_status] => any,
[post_type] => attachment,
[post_mime_type] => application,video,text,audio,image,
[suppress_filters] => 1,
[post_parent] => null

Settings posts_per_page to -1 gets you the full list in the correct order.

This has been broken since at least 4.3.x.

[pento]

See Slack discussion: ​https://wordpress.slack.com/archives/meta/p1448577626000264