DJ Jeff
Not so Jazzy
The agreement was that Swansea could sell if it was in the best interests of the club to do so. They obviously thought £15 million for Joe Allen was good business & were quite happy to take the money.
Taken from the BBC at the time:
Although the new Liverpool manager has a written agreement with Swansea not to return to his former club to try to sign any of their players for the next 12 months, the Welsh club can waive that clause if a deal is deemed to be in the best interests of the club.
It would seem the best interests of the club were to get rid of the player who was now unsettled and unhappy because his former manager had come in for him despite his promise not to.