this one seems to be bugged.
the hotkey definition is there in the preferences, but it’s not valid for actual usage as it seems:
[url=http://www.abload.de/image.php?img=clone_seq77a7.png] 
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Hey keith,
there are several clone shortcuts in various parts of Renoise, which indeed a bit confusing. The one you highlighted in the pattern sequencer is “Clone Selection” in the “Pattern Sequencer” shortcuts sections. Try searching for “clone” in the key bindings to see them all…
ah, silly me.
thanks for giving me the hint, taktik 