It's to do with a dodgy valve, apparently. Subject item was installed on a DC-10 in 1999, but had been incorrectly assembled. Caused an uncommanded deployment of the reversers (possibly only partial, as the aircraft did not suffer an extreme loss of control, as the Lauda Air 767 tragically did a few years ago)
Now, why it did not fail on installation is a mystery, but that's the situation as it is at the moment. Presumably once any suspect valves have been identified and isolated, the restriction can be lifted.