Cannot create fingerprint. (Possible OpenSSH 6.6 implementation bug?)

I’ve problems adding an SSH key to my gitlab server trough the API (It works well trough the webpage).

Gitlab information:

I came across this issue which was related to an “wrong” openssh implementation. They’ve fixed this in milestone 7.10. Only thing… My server has openssh 6.6 installed:

OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.3, OpenSSL 1.0.1f 6 Jan 2014

Now, I don’t know if that fix is backwards compatible or not, but maybe good to mention.

Also, the logs show no warning or errors or whatsoever. The /tmp/gitlab_key* files are generated on the server:

So right now I have no idea what the problem could be. I’ve been struggling with this for almost a week now, so I really hope that his problem could be fixed.

-just for the record, here’s the script I’m using to add the ssh-key trough the API