Microsoft said today it has determined what is causing some Windows Phone 8 devices to spontaneously reboot and said it plans to issue a fix next month.

"We're continuing to investigate some reports of phones rebooting and have identified a cause with our partners," Microsoft said in a statement. "We are working to get an over-the-air update out in December."

However, the company declined to identify the cause of the reboots.

The issue materialized earlier this month when some users of Windows 8 devices complained of spontaneous reboots and e-mail sync issues. ZDNet's Mary Jo Foley described an unexpected reboot of her loaner HTC 8X Windows Phone 8 on AT&T, as well how her e-mail accounts and Microsoft Account were stuck in an endless loop continually trying to sync. However, her Windows Phone 7 handset was not experiencing these issues.

Some users on forums claimed that uninstalling the Skype for Windows Phone 8 preview app, which Microsoft released a week earlier, may fix the rebooting issue. However, some users were complaining of reboot/sync problems before the Skype preview for Windows Phone 8 app was available publicly.