In the craziness that was the winter holiday travel season—one that left thousands of airline passengers stranded as a bomb cyclone gripped the country—a minor airport inconvenience may have slipped under the radar: Many Colorado driver’s licenses won’t scan at Transportation Security Administration checkpoints.

I first discovered this for myself while flying out of Ft. Lauderdale a couple of weeks ago when, already late to catch my flight, the TSA agent took one look at my license and said something along the lines of, “Ugh, Colorado IDs are the worst. They never scan.” Sure enough, I watched as the agent’s Credential Authentication Technology (CAT) machine, the little black box on her desk with a slot similar to an ATM, rejected my license and forced her to verify that I was who I said I was manually (which appeared to be only slightly more intensive than what a bouncer would do at a bar).

Back in Denver, I asked friends and co-workers if this had ever happened to them, and the answer was a resounding: all the time. “I’ve had TSA agents get legitimately worked up about it before,” one colleague told me, “and then proceed to take their frustration out on me.”

The problem doesn’t appear to be with Colorado’s licenses, which meet the latest standards, according to a Colorado Department of Motor Vehicles spokesperson. Nor does it have to do with the costly and controversial switch to REAL ID. (You’ll know you have a REAL ID by the star on your license.) It has to do with the CAT machine itself and the database it references.

“CAT units are not dedicated to reading REAL IDs,” says Lorie Dankers, a TSA spokesperson. “They were not rolled out because of REAL ID.” Though she does admit that many travelers think so given the concurrent timelines for the adoption of both technologies. Instead, CAT units are do-it-all machines that can read multiple types of identification—including military IDs, passports, and Global Entry cards—and link them to your flights so you no longer have to scan your boarding pass. (When the CAT machine accepts your license, that is.) This supposedly saves individual travelers seconds or minutes and cumulatively speeds the entire security line an hour or more over the course of a single day.

And the machines don’t just read barcodes. A major part of the technology’s purpose is spotting fraudulent IDs, and it does so by scanning the whole license and measuring minute details (such as letter spacing) against a database. And that’s where the problem lies: There appears to be some discrepancy between the legitimate IDs many Coloradans have in their pockets and what’s in the TSA database.

Dankers wouldn’t elaborate. “We’re not here to provide a roadmap for counterfeiters,” she says. The agency is working to update its system, which happens regularly, but there is no timeline for a fix. Until then, TSA agents will just continue to verify our identities the old-fashioned way.