Isn´t this command supposed to make the duplication in the destination lister, which is on the other side? The new tab will open in the same lister side. 
Try this instead:
Go OPENINDEST TABDUPLICATE=dual
Ah, that was it, thx, John. 
By the way, is there a way to set that duplicated tab to be the selected & active one, in the destination? I can´t find any useful hint about this.
Well I would expect the following to do it, however Opus seems to not take in account the newly created right side tab when it selects the last tab. Instead it selects the tab that was last before the duplication.....hmm..
Go OPENINDEST TABDUPLICATE=dual
Set FOCUS=Right SOURCE=Right
Go TABSELECT=last
This seems to work:
Go CURRENT OPENINDUAL NEWTAB=tofront
Set FOCUS=Toggle
Edit: HOWDY JOHNZ!
Cool, this works. Thanks steje.
Yo steje, long time no yo. 
Glad to see you found a way to solve abr's dilemma, I have to admit I hadn't tried that combo yet.
[quote="JohnZeman"]Yo steje, long time no yo. 
Glad to see you found a way to solve abr's dilemma, I have to admit I hadn't tried that combo yet.[/quote]
Thank both of you guys. Opus´ abilities are like a jungle.