libssh 0.7.5-2 on Arch Linux.
When I force Kex to diffie-hellman-group14-sha1 plus any other algorithm, ssh_options_set report a "invalid value" error.
Specifying only diffie-hellman-group14-sha1 works without any issues.
This happens in the Remmina code I've implemented, as I didn't try to use the available examples, I cannot exclude it's my fault...
Let me know if you need additional infos.