The Material Girl has made a point to pay tribute to her late friends and famous peers -- including Herb Ritts, Freddie Mercury, and Keith Haring, all of whom died from AIDS-related complications -- with a photo montage amid her performance of "Live to Tell."

During Saturday night's tribute at Madge's Sacramento concert, a photo of the late soul singer was included -- despite the R&B singer's 2005 death previously being attributed to complications from a prior stroke.

In fact ... Luther was actually defensive about this rumor about him while he was alive ... once even going after a British magazine back that tried to pin his weight loss in the mid-80s to the virus. So yeah, it's a sensitive topic.

While Luther's camp acknowledged Madonna's effort to honor those who've lost their lives to AIDS ... they emphasized to Page Six that the late soul singer was never diagnosed with AIDS or the HIV Virus, and it sounds like Luther's estate kindly asked her to exclude him.

Madonna has since scrapped the photo from the tribute ... after Luther's estate reached out to her management team, so all's well that ends well. Seems like an innocent mistake.

For those wondering ... Luther's sexuality has long been speculated on -- but he never came out as anything other than heterosexual ... although, close friends of his have commented on this in the years since and suggested he may have been part of the LGBTQ+ community.