The case was Administrator v. Merrell, in which Merrell's readback of an instruction to another aircraft was blocked by the other aircraft's acknowledgement, and Merrell executed that instruction, resulting in the filing of a Pilot Deviation Report. The three NTSB hearings on that case are:"We're logging this as a controller error and not a pilot error because the burden is on the controller to ensure that the pilot's read-back is correct," Gregor said."
That does seem to recant an earlier ruling (someone will have to find that for us) where the pilots are at fault even if the controller did not correct a bad readback. 'I remember us saying, why do we have to readback if they are not obliged to even listen?'
Under the Administrator’s interpretation of the relevant regulations, however, an error of perception does not constitute a reasonable explanation for a deviation from a clearly transmitted clearance or instruction. Rather, inattentiveness or carelessness is presumed from the occurrence of a deviation unless, as we understand it, the misperception or mistake concerning the clearance was attributable to some factor for which the airman was not responsible, such as an equipment failure.[emphasis added]