After upgrade to Plasma 5 (Kubuntu 15.04), one of my regular sftp locations in Dolphin is no longer working.

Qt: 4.8.6
KDE Development Platform: 4.14.6
Dolphin: 14.12.3

Initially, the error message was:

The host key for this server was not found, but another type of key exists.

I removed the server from known_hosts using ssh-keygen (plus the underlying IP address), and dolphin then prompts for confirmation with a fingerprint, but it doesn't match any of those on the server (checked rsa, dsa, ecdsa). If I connect in a terminal with ssh, the correct fingerprint is displayed.

Connections to other servers are all fine. After reading some other posts here, I tried fish: in dolphin and that seems to connect fine.

ssh user@host.domain (terminal) - Fine, correct fingerprint.
sftp://user@host.domain (dolphin) - incorrect fingerprint offered or no access
fish://user@host.domain (dolphin) - Fine.

Obviously I didn't accept the bogus fingerprint at any point, but I assume it would connect then. I can switch to the fish address, but it looks like something is between dolphin and the server which is worrying.

How can I see what's intercepting and changing the fingerprint?

Late after your post...

Had same problems connecting dolphin with sftp.
I checked my /home/$USER/.ssh/known_hosts
and it was owned by root:root with rights 600.
Happened on Kubuntu 16.04.3 LTS after package upgrade.

Corrected with:
sudo chown $USER:$USER /home/$USER/.ssh/known_hosts
sudo chmod 644 /home/$USER/.ssh/known_hosts