"Preview Email" function doesn't work

I'm trying to send a test/preview email using the settings page, but it isn't working. Clicking the "send a test email to:" button just saves the Settings instead of sending the email! (Basically the same as if I'd clicked the blue "Refresh changes" button)

They are both type=submit buttons, so i'm not surprised this is happening, but how can I actually send a preview email?

I'm using WP 3.9.2, the latest SbE plugin, and using Firefox v31