It's a monotype font, so I expected to see it across all Windows of the internal editor, but that's not the case.
When a file starts with certain characters, the editor changes to some other non-monotype font that makes it hard to read the file (a log file in my case).
I'm using characters from the Extended ASCII to make a header:
Once I change the first character to, let's say, "X", the font is correct:
Point to mention: while the incorrect font is showing, if I click the Settings icon in the editor and change the font size to anything else, then once I close the Settings window, the correct font will be applied, until I close and reopen the file.