On my board, after typing anything, copy or paste option on right click of the mouse shows only once. After that, right click does not display the option. However, the Control C and Control V for copy and paste works.
I noticed that if I disable the "insert Hyperlink" button in theme options with "WYSIWYG" changed, then the right click works correctly but the Insert Hyperlink button does not work. So one or the other works and this is irritating to all my members.
Let's be honest about this...
The WYSIWYG editor is a bug-ridden pile of poo, I'm afraid. :(
It's being revamped, for the next version of SMF. So, you might want to disable it, in your profile.
If it's any consolation this WYSIWYG problem also occurs on other makes of software I've worked with. The solution was the same as K@ has said.
Thank you both!
Just sorry that we could be more helpful. :)