The crew may have said there was a "radio problem" but the most likely outcome is that the problem was caused by a bumped setting on the ACP.
Because the radios were serviceable (proof: they worked just fine once on ground) they didn't bother to snag anything in the logbook and the radios were never inspected, until the full gravity of the situation came to light after the ASR was sent in.
They'll get a stern talking to by the Chief Pilot and both pilots will promise to never, ever do it again. Case closed.