psql hangs after "drop table ..."

I'm trying to drop an empty table (0 records) using:

testdb=> drop table empty_table;

but psql just hangs indefinitely after I hit return. No error
messages. (The table definitely exists; no other table refers to it.)

The only way out is to hit Ctrl-C; when I do this I get the message:

Cancel request sent
ERROR: Query was cancelled.
testdb=>

What's going on? What can I do to troubleshoot this problem?

Thanks!

kj