OnContextMenuRequested not called at every times

Both the method and event will fire whenever the SyntaxEditor control gets WM_CONTEXTMENU. I just verified the code. However they will not fire when one of the scrollbars gets a right-click since those are separate controls.

I re-enable the default context menu and I still got the problem. It happened more often when the cursor is at the beginning of a line.

Can you give us detailed steps on how to reproduce it in the sample project? Thanks!

No, I can't reproduce it in the sample editor.
But I get the way to reproduce it in my application. That's a determined square at the top left of the control.
I know you can't do anything since the problem doesn't seams to be on your side, but if you have a clue to me, don't be shy.

I'd love to help if I can but on our end, we respond to the WM_CONTEXTMENU message. So if something is intercepting that in your app, then that could cause it not to show. I'm not sure what would do that though unless you had some other control over SyntaxEditor.