DROP INDEX hangs

Hi all

Using PostgreSQL 9.3.4, compiled by Visual C++ build 1600, 32-bit (on
Windows, obviously).
I noticed that my vacuumdb was hanging on a specific index, so I decided
that the easiest path was to create a duplicate of it (CREATE INDEX
CONCURRENTLY myindex_v2 ...), and drop the original one (DROP INDEX
myindex).
Bad idea : the DROP INDEX command is hanging, doing no IO but using a
full CPU core.
It does not look like it is waiting for a lock (pg_locks show very few
locks right now, and absolutely none related to this pid).

The index is not listed anymore in the table description though
(something was definitively wrong with this index).

I tried to nicely cancel the query via pgadmin, but this does not help.
What can I do ? Should I terminate this backend ? What is the risk of
terminating a drop index operation ?

Thanks for your advices !

--
Arnaud