Patch for bug 2592809 (Freezes Entire Desktop). This patch prevents the Enter key from popping up the combo box list when the combo box has focus. The Enter key instead simulates pressing the Connect button, which is the dialog's default action button.
Without this patch, the Enter key effectively does both. In doing so, it launches the remote session, but also pulls down the combo list and blocks all mouse input pending its dismissal. However, dismissal is impossible while the remote session is active because the dialog is hidden.
Attribution: patch developed by Mick Kemsley and posted to Ubuntu Launchpad board: