One of our testers brought this to my attention today and I feel like we must be missing something. If you have the setting "Double-click opens messages in new window" checked, the windows that result from a double-click don't have any options such as Reply or Accept (for calendar meetings). If you also have the "message reading pane" disabled, that means there is no way to have a single view that provides both the message text, and the action buttons like Reply. You have to read the message in the new window, then go back to the main window to reply to the message.
It seems like these new windows should have the same action buttons found elsewhere. Is there an existing bug/feature request for this (I searched and didn't find anything) or am I confused and/or missing something obvious?