NEW YORK (CNNMoney) -- Facebook already annoyed its users by automatically posting their @facebook.com addresses to profiles and displaying them as the default. Now the problem has spread to some users' mobile phones.
A handful of CNNMoney readers wrote in last week after news of the @facebook.com email "update" to complain about problems with phone contacts that are synced to Facebook accounts.
After several news reports, Facebook confirmed on Monday that the problem is real. The company says it was caused by a bug in the contact-sync system for some phones.
"For people on certain devices, a bug meant that the device was pulling the last email address added to the account rather than the primary email address, resulting in @facebook.com addresses being pulled," Facebook said in an e-mailed statement.
Facebook (FB) didn't name specific devices in its statement, nor did it explain further about the "bug." The company says it's fixing the problem and "it will be resolved soon."
The mobile bug is fanning the flames of Facebook's email debacle. While every Facebook user has an @facebook.com email address -- whether they use it or not -- the service doesn't seem to have taken off. Some characterized the change as a ham-fisted way for Facebook to push its email system, which it first announced in in late 2010.
Facebook denied those claims to CNNMoney last week, saying its goal was simply to add "consistency" how email addresses are displayed on members' Timeline profile pages.
Whatever the company's intention, Facebook users don't tend to take kindly to major changes with no prior warning.
California resident David Thomas, who owns an HTC Incredible that runs on Android, is among those who contacted CNNMoney about the glitch.
Thomas says he didn't even mind the @facebook.com change on Facebook's website, but the mobile problem sent him over the edge.
When Thomas fired off an email to a contact, he was startled to find the @facebook.com email swapped in as the default address.
"Talk about an invasion of privacy," Thomas wrote."I don't want to write to people's Facebook e-mail address... they probably don't know they have one."
The bug is sporadic. It didn't affect several Android phones that CNNMoney tested, but it did show up on a Nokia Lumia phone running Windows 7. Some iPhone users who have upgraded to iOS 6 also reported the problem.
There's no easy fix yet. A frustrated Thomas went through and manually reset the contact information for each of his 40 Facebook-synced contacts.
"Everything has been fine since then as far as I know," he wrote. "Thankfully, not all my contacts are linked to a Facebook profile and those were unaffected." 
