I've seen too that groups cover picture has the same problem !!!!!
Cancel and save buttons are not translated like for event cover picture, they are called "Undefined"

ANOTHER TIME I CAN MODIFY PROFILE COVER PICTURE !!!!!!!!!!!!!!!!!!!!!!!!

I can load the window popup window, then choose the picture I've loaded then i click on the picture, the picture is added in cover form (the first time buttons are not translated), I click on undefined, the picture seems to bo well added but when refreshing page, the default picture is reloaded.

If i click again on modify profile cover picture, and choose directly the picture loaded before, then this time, buttons are well translated but it's the same problem! The worst is that in activity stream It says user has modified it's cover displaying good picture but the profile hasn't it !!!!

IT WORKED FINE THIS MORNING AND I DIDN'T CHANGE ANYTHING !!!!!!!

Check on my production server. I give you access reediting that post.

Finally I've seen that the problem of cover picture only happens with that user that i told you

It's stange because I changed picture to 1140x428 and it's the same. It only happens with that user

Ehm, weird, so this issue only happens on one user? and not happens on another user? can you provide me that user who has this problem? seems I lost that account. thank you