According to an insider, Kidman has been going back on her word and never finishing things she starts, from major projects, like film projects, to the most minor of items, such as returning phone calls.
"Nicole's flakiness aggravates Keith to no end," the insider told RadarOnline.com.
Unfortunately, for Urban, 50-year-old Kidman's problem is only getting worse with age.
"The older she gets, the flakier she becomes," noted the insider. "She says she'll take care of something and then she doesn't. She's got so much on her plate that she can't keep track: career, kids, even her husband!"
"She'll be talking to Keith on the phone long-distance, put him on hold and then forget about him," laughed the insider. "It makes Keith grind his teeth so much they'll be nubs if this continues."
As RadarOnline.com reported, Kidman's annoying tendency to flake is just the tip of the iceberg when it comes to problems between the Beguiled actress and the singer, who just celebrated their 11-year anniversary on June 25.
Sources revealed that the angry Aussie's terrible temper has gotten so bad in recent weeks that her 49-year-old husband had a "rage room" installed in their Nashville, Tenn., home.
Too bad it's not just the country crooner who has to deal with Kidman's irritating issue.
"Nicole is notorious for backing out of film projects, too," said the insider. "She'll say yes, she'll consider something, and then she'll drop the ball and send producers scurrying for new options."
We pay for juicy info! Do you have a story for RadarOnline.com? Email us at email@example.com, or call us at (866) ON-RADAR (667-2327) any time, day or night.