An Oxfam worker fired over sexual misconduct allegations in Haiti was rehired later the same year by the charity.
Oxfam said its decision to rehire the man in Ethiopia was a "serious error".
It said it was still looking into how the decision had been made and whether there were "any issues" while the man was working in Ethiopia.
Oxfam has faced mounting criticism over the way it handled claims staff used prostitutes in Haiti in 2011.
The charity's own investigation in 2011 led to four people being sacked, including the man who was rehired, and three others resigning.
The man who was rehired worked in Ethiopia from October to December 2011.
In a statement, the charity said the rehiring error highlighted that "an organisation and sector-wide approach" to recruitment and the vetting of staff and consultants was needed, "especially in emergencies where there is pressure to fill posts quickly in order to help save lives".
Separately, the former Oxfam director accused of hiring prostitutes while working in Haiti and Chad, Roland van Hauwermeiren, has denied paying for sex but admitted some "mistakes".
He said he had "intimate relations" with a woman in earthquake-stricken Haiti who was "not a prostitute".
On Thursday, International Development Secretary Penny Mordaunt met law enforcement officials to discuss how vulnerable aid recipients can be protected from abuse.
The National Crime Agency said the "productive" meeting discussed how to guarantee "appropriate safeguarding provisions" were in place.
The Charity Commission also gave details on the scope of its statutory inquiry into Oxfam, saying it "will establish the facts about what the charity knew about events in Haiti in 2011, and how it responded at the time and since".
It added that the inquiry will seek to "understand Oxfam's overall approach to safeguarding," in order to uphold trust in the charity.
Meanwhile, Archbishop Desmond Tutu has become the latest high-profile figure to end his ties with Oxfam over the scandal.
In a statement Mr Tutu said he was "deeply disappointed by allegations of immorality and possible criminality involving humanitarian workers linked to" the charity.
He added that he was stepping down from his role as a global ambassador.
In the wake of the revelations, first reported in the Times newspaper, Oxfam's deputy chief executive, Penny Lawrence, resigned.