Funny, it seems on several web pages I've encountered the only way to bring up the menu is to hold the control key and click the physical mouse. VO+shift+m does not work in these cases at all.
I suspect that these situations are bugs! But in order to rule out user, please provide a URL for the problematic link target in question. The bug could be with VO or Safari or may be related to less-than-accessible JavaScript. I think clicking with Mouse Keys will be reliable in these situations. This is a problem that warrants deliberative investigation.
