- version changed from SVN (CKEditor) - OLD to 3.4.2 (SVN - trunk)
Fred, this is an easy fix and an important bug :)
In plugins/contextmenu/plugin.js, the addTarget function
if ( CKEDITOR.env.opera )
could be for example (slightly different suggestion from above)
if ( CKEDITOR.env.opera && ! ('oncontextmenu') in document.documentElement )