Stefan,
I try to use a private key newly generated with PuTTY Key Generator (RSA 2048 w/ passphrase) but when I try to connect to a server it crash RTS with a message:

Additionnaly, I noticed that the Passphrase field (thas is not a password field so you can see the passphrase
) in the connection properties isn't stored and is empty when you reopen the property dialog...
You may have received 2 bug reports for this
(the first with an OpenSSH key converted to PuTTY format, the second with the newly created one)
Let me know if you need more infos !