The U.S. Postal Service unveiled a limited edition stamp honoring poet and civil rights activist Maya Angelou at the Warner Theatre in Washington, D.C. The first lady Michelle Obama, Oprah Winfrey and Attorney General Eric Holder were amongst those in attendance. (Reuters)

The U.S. Postal Service on Tuesday released a new Maya Angelou stamp featuring a quote from a different author’s book, propagating a popular misconception about the original source of the line.

“A bird doesn’t sing because it has an answer, it sings because it has a song,” the stamp reads.

Angelou, the late African-American author who wrote the famous 1969 autobiography “I Know Why the Caged Bird Sings,” used the same line in media interviews, and President Obama attributed it to her during the 2013 presentation of the National Medal of Arts and National Humanities Medal.

But the sentence never appeared in Angelou’s autobiography. The words came from Joan Walsh Anglund’s collection of poems, “A Cup of Sun,” published two years before the release of Angelou’s autobiography. (One difference: The pronoun “it” from the stamp quote appears as “he” in the poem).

[Book author Joan Walsh Anglund says of Angelou stamp: ‘That’s my quote’]

Nonetheless, the Postal Service moved forward with its release of the stamp at Tuesday’s event, which featured dignitaries such as first lady Michelle Obama, Oprah Winfrey and the poet Sonia Sanchez.

USPS said it didn’t know about Anglund’s book until Monday, when a Washington Post article pointed out that the quote in question didn’t originate with Angelou.

“Had we known about this issue beforehand, we would have used one of [Angelous’s] many other works,” USPS spokesman Mark Saunders said in an e-mail on Monday. “The sentence held great meaning for her and she is publicly identified with its popularity.”

“The Postal Service puts a great deal of time and energy into vetting the stamps it releases each year,” Saunders added in a follow-up email. “This stamp was similarly vetted. We found that the phrase was widely attributed to Angelou in many mediums and by some dignitaries and we were not aware of Ms. Anglund’s 1967 book.”

For what it’s worth, even the title of Angelou’s autobiography comes from another writer, prominent African-American poet Paul Laurence Dunbar, whose poem “Sympathy” included the line. (Correction: The Federal Eye made a mistake of its own here, incorrectly attributing the hymn “Lift Every Voice and Sing” to Dunbar in an earlier version of this article).

The release of the stamp comes less than four years after another fumbled attempt to honor an historic African-American figure. Controversy erupted in 2011 over an abbreviated quote on the Martin Luther King Jr. Memorial that critics thought would make the civil-rights leader appear immodest.

One of the inscriptions on the memorial read: “I was a drum major for justice, peace and righteousness.” But King actually said, “Yes, if you want to say that I was a drum major, say that I was a drum major for justice. Say that I was a drum major for peace. I was a drum major for righteousness. And all of the other shallow things will not matter.”

Angelou, who died last year, said the abridged version made King sound like an “arrogant twit.” The Department of the Interior initially considered sandblasting the inscription and replacing it with the full quote, but the agency ultimately decided to remove the line altogether.

* Lonnae O’Neal and Magda Jean-Louis contributed to this report.