The right-click paste option does not seem to work for password field on remote desktop connections.   Only the Ctrl-v option or manual entry of the password seem to work.  The link below is an additional reference to the issue:

https://social.technet.microsoft.com/forums/windows/en-US/e67338f0-b5cb-4f50-829a-bb19f2778835/remote-desktop-connection-mstscexe-password-paste