We bought an old pendant light for our flat, with a two prong plug. Rather than rewiring it in to the existing outlet, I just bought one of those $2 lamp holder outlet adapter. To be on the safe side, I checked it with my contact volt tester, which lit up when it came within a few inches of the unit (not even in contact).
I plugged the pendant in to a standard wall fixture and all was fine (no charge on the casing, the tester only lights up with contact on the cable). What's more, when I plugged our bedside lamp in to the ceiling adaptor the same thing happened - a good 2-3 inches out the fluke lit up.
Is there something about those outlet adapters which may be causing the pendant and lamp to be live? Or perhaps the ceiling fixture is rated too high for the pendant and lamp?