Did you know if you select multiple items in Mozilla Thunderbird and press Delete followed quickly by enter, Thunderbird deletes the messages and then opens multiple empty message windows?
You can often find unexpected behavior when you trigger two actions at once that the user would never do, such as this particular thing I always do.
In Web testing, you can do this using the Enter key to trigger one button while clicking another or by clicking multiple buttons in quick succession.
In mobile testing, you can do this by tapping two things at once or making two gestures at once. Or by Doing something and pressing the Home button or the Power button.
In desktop application testing, this can be by clicking a button while pressing a hot key or pressing multiple hot keys at once or in rapid succession.
Regardless, the application should always pause other input while taking an action and should always check to see if it has everything it needs to act on when starting an action. In this case, it would be an active, not deleted message.