Hi.
I have attached my current gutter and enabled parts as from the object inspector. Of course, I have removed the blue background color from the gutter.
I removed the autosize from the mark part, because I need exactly two marks with 16-by-16 (one for the bookmarks 0..9 and one for my linetype marks). I don't need that part to be flexible in size.
Interestingly: I have made a new form with a naked SynEdit and adjusted it with my settings. It has the same strange thick line on the right. Then I changed the left offset from 10 to 0 and the thick line to the right is not there any more. I previously thought that the left offset makes some distance to the mark part, but it installs it on the right side.
Case closed. Thanks again for your assistance.
brgs, gsc