In Windows 7, if you pin a program to the taskbar, then when you launch the program, Windows 7 will group your program’s window icon into the taskbar icon and change the taskbar icon’s style so you can tell that an instance of the program is running. However, I recently noticed that Windows Live Mail does not follow this rule. When you launch Windows Live Mail, a new window icon is created in the taskbar, so there are two Windows Live Mail program icons in the taskbar. See the attached screen shot.
However, Windows Live Writer does follow the rule. Maybe it is a minor bug in Windows Live Mail. I will report this issue to Windows Live Team to see what they explain.