The reason being it is a plain text edit component, with a window around it, hence the limitation.

Yep. Back when I used to teach Windows programming in C commercially, the course exercise was to replicate notepad. It was surprising how many of its features you could implement in a week-long course, especially as many of our clients were no great shakes at C.

I think it is more surprising how many deeper features were hidden in Notepad (I did a complete re-implementation using MFC for Windows CE).

Did you implement .LOG and Unicode support with BOM handling?