Solved. It comes from File Description as I guessed. Windows caches the name so I cleared the cache.

DETAILS:

1. The name, which is shown when you right-click the app task in taskbar, is called "Friendly App Name".
2. Windows uses File Description as Friendly App Name.
3. Windows caches Friendly App Name on first launch in registry at HKEY_CLASSES_ROOT\Local Settings\Software\Microsoft\Windows\Shell\MuiCache

REFERENCE:

• The AssemblyTitle never changes once set, I want it to be changed per configuration