In my 'Taskbar' I use icons only, flat buttons and combine multiple applications into one button.
If you look closely you can see that the icons of the task bar don't have the same size as the icons in the system tray:
I like to see that fixed.
This behavior is not bug but feature. If you make icons on task buttons equal to icons on other plugins then they will be cut by task button relief borders, so these icons are made a bit smaller deliberately. Thank you very much.