After upgrading and moving to a new host, we got wp 3.8.1 and domain mapping activated on our multisite.
When viewving events the featured image url gets mixed up, and image url is wrong. it tranlate its url to the event post, and not to the image directly, but with the image filetype at the end. ex. ../filename.png/ as the default url structure end.
We did´t have this issue with another multisite, but on that server the media url was not translated to the mapped domain.
To the record, featured images works correctly on post/pages.