@Henppy
You have to go to the Object Inspector, and select "SynEdit1>KeyStrokes", then change the Shortcut number 64, 65, 66, ..
They are set to ecSetMarker0, ecSetMarker1, ...
You should change them to ecToggleMarker0, ecToggleMarker1, ...
@Martin,
I have found that when using the BookMark Shortcuts (enabled by default) with no assigning a ImageList to: "SynEdit1.BookMarkOptions.BookmarkImages", the SynEdit, crashes. At least in my system. Is that normal?