The appointment of the late MP Tobias Chukwuemeka Okwuru to the Federal Character Commission emerged when a letter of confirmation from Mr Buhari was read to the Senate.
Applications were quickly reopened after journalists pointed out that Mr Okwuru was not available to take up the position due to his death at the age of 59.
A spokeswoman for the president blamed a lengthy screening process for the confusion.
By Jane Flanagan. The Times
Few people are surprised that delays were implicated: