This makes sense is the focus is off of the original message window but I can't duplicate it. Focus always returns to the original message window after sending a reply and the M button works. I thought perhaps focus would change after doing a copy to self on the reply but even then the focus returns to the original message. I run Pegasus (v4.62) windowed (stretched to full screen) in List mode but tested both windowed and maximized.
This makes sense is the focus is off of the original message window but I can't duplicate it.  Focus always returns to the original message window after sending a reply and the M button works.  I thought perhaps focus would change after doing a copy to self on the reply but even then the focus returns to the original message.  I run Pegasus (v4.62) windowed (stretched to full screen) in List mode but tested both windowed and maximized.