It is a fact universally understood that gifted performers tend to be at their very best when on stage and scripted.

Bill Murray gave a terrific two-hour performance Tuesday night at Symphony Center, where his show “New Worlds: Bill Murray, Jan Vogler and Friends,” a unique blend of dramatic performance and music, played to a packed house. A post-show CD signing apparently went as planned, too. And things continued in a perfectly fine way as audience members, who had paid $150 (in addition to the price of a concert ticket) in order to attend a post-show gathering in the theater’s Buntrock Hall, waited to join Murray for pizza and beer.

According to Sean Kennedy, 35, an attorney who had treated his brother to the concert and post-show event for his birthday (the post-show party was a benefit for the CSO Association), some of the 100 or 150 people or so with post-show tickets headed to the food tables before Murray’s arrival, while others lined up so that they could have their photo taken with Murray by a professional photographer. (The picture would later be posted on a special online site available to the party-goers.)

“Murray posed with couples and others for about 20 or 25 photos, then saw people he knew in the crowd and went over to chat or hug them, then came back to do another 20 or 25 pictures,” recalled Kennedy. “By the third time he came back to continue with the photos he had pizza in his hand . And he had already turned away one woman who was shooting pictures with her cell phone. Meanwhile, by now the idea was that the professional photos would be taken with larger groups. And when a woman demanded that she wanted one with just her and her husband, instead of a group of strangers, he yelled at her to get out. I think some people thought he was kidding at first, and she was embarrassed and moved to the side. But he was serious.”

Kennedy wasn’t making excuses for Murray, but said he was “somewhat sympathetic.” And he added that once the actor abruptly left the room, the three musicians who had played with him followed suit.

“It was a great show, and he’d been to the Cubs game the night before,” Kennedy said. “He was probably just tired.”

Kennedy and his brother, who were toward the back of the pack, never got a photo (“We were about 10 people away from [Murray] when he left”), but he did request the refund that was offered, noting “The CSO people were very sympathetic and understanding about it. I haven’t seen the refund on my credit card yet, but that’s likely just my credit card company.”