Yes, reinstalling and activating from the main blog got Quick Cache up and running in a jiffy. Wonderful.
The problem mentioned happened when installing and activating from a sub-site -- like I mentioned before -- but also in combination with WPMU Domain Mapping and the sub-site in question had a TLD (different from the main site TLD) set as its primary domain... Just to add some complicating factors to the matter ;)
Don't think it would be a common thing for anybody to run into so I'd not mark this as urgent. Anyway, thanks for your support and interest in improving your excellent plugin !