Invalid image path returned

[tom-henderson]

Wordpress 4.0 with multisite enabled, plugin version 3.1.13.

Adding a featured image to a post is saving an invalid image path:

Array
(
    [0] => Array
        (
            [thumb] => http://www.example.com/wp-content/uploads/sites/10http://www.example.com/foxglove/wp-content/uploads/sites/10/2014/08/ballroomopiumden044-150x150.jpg
            [full] => http://www.example.com/foxglove/wp-content/uploads/sites/10http://www.example.com/foxglove/wp-content/uploads/sites/10/2014/08/ballroomopiumden044.jpg
            [attachment_id] => 
        )

)

Existing featured images saved to posts are displaying correctly. I'm not sure if the issue started after upgrading Wordpress or the plugin.