the "Toggle Marking" function you are using is in the logger section of the context menu/ribbon and highlights all messages with the same logger as the selected message (also highlights the specific logger in the tree with the same color).
I assume you want to use the bookmark function for single specific lines? You can find this functionality in the context menu's "Bookmarks" submenu and the ribbon. You can also just use F4 to bookmark the selected message and Ctrl+F4/Ctrl+Shift+F4 go jump to the next/previous bookmark.
By the way: does "Toggle Marking" really change nothing in your scenario? As mentioned, it should highlight the selected message, its logger and all other messages of this logger.