DJ Steve Wright's weekly dedication show is ruled to have breached BBC guidelines after Radio 2 listeners were encouraged to leave requests for programmes which had already been recorded.
The audience was told on air they could get in contact with the Sunday Love Songs programme "any time", without an explanation that the show's script had been finalised days earlier.
It meant some listeners wasted money on calls, and their requests for romantic messages to loved ones had already missed the cut-off point.
The BBC Trust's editorial standards committee said the failure to inform listeners properly breached guidelines on accuracy and interacting with the audience.
It came to light after listeners to one edition were informed the show was pre-recorded rather than live - and only then to make it clear that a reference to entertainer Andy Williams in the programme had been recorded before his death, which was announced on the day of broadcast.
A listener complained that some callers who had been encouraged to make requests would be wasting their efforts, as were some who listened in hoping to hear their letters read out and songs played.
The show is actually recorded on a Friday, but the playlist and script are completed by Thursday and listeners were not told there was a cut-off point. An answerphone message for callers only made it clear after they had already left a request.
Radio 2 went on to change the on-air and phone messages, but the Trust said these did not go far enough and should be amended further to make clear that calls made after a certain point in the week would not be considered for the next show.
The committee upheld the listener complaint about accuracy and interacting with audiences. However it said the problem was "essentially one of a lack of clarity", rather than an effort to intentionally mislead.
A spokeswoman for the station said: "In light of the Trust's findings on clarity for people leaving dedications for the programme, we have revised the wording in order to ensure the process is absolutely clear for listeners."