Hi @Gijs,
As Windows doesn’t support single line fonts, they are fudged by superimposing the two sides of each stroke, rather than placing them a stroke width apart. (It’s actually rather more complicated than that.) That may be resulting in what you see. The problem, in a nutshell, is getting the balance between ‘duplicate’ lines - which are needed for the font to render as a font in the textbox - and single lines - which are all the tool needs.
Regards
Jeremy