If you have this kind of problem then that means you pinned Notepad++ to the taskbar, when the change.log file was open. This made windows pin that file specifically, rather than just starting NPP. So when you started it by clicking the icon, you were opening “change.log” within it.
To solve that problem right click on the notepad++ icon in taskbar and go to properties. And change TARGET of the shortcut. Probably your target of the notepad++ shortcut looks like this (FROM part). Make it as (TO) part.
"C:\Program Files\Notepad++\notepad++.exe" C:\Program Files\Notepad++\change.log