In Bitcoin Qt, I tried to lock unspent outputs. My intention was to lock all but one to force a particular output to be selected for a transaction.

I understand it should work like this:

• call lockunspent with a list of outputs
• call listlockunspent and observe that all specified outputs are actually locked

Unfortunately, none are locked in my testing. What am I doing wrong? There was no error message. I entered the command in the debug window.

Edit: I reviewed the source code and I did not find any obvious usage errors on my part. Debugging the client is beyond my abilities, though.