If you’re missing email messages, don’t blame Facebook: The social network says you are simply “confused.”

Facebook spent a second straight weekend dealing with complaints from users about a switch in the default user email addresses, this time with users complaining that the change was resulting in lost messages and contacts.

Several bloggers and users raised complaints late last week and over the weekend about missing messages. But a Facebook spokesperson said the missing messages may stem from confusion over how Facebook’s mail system categorizes messages, and that engineers were looking into complaints about a phone syncing issue that made it appear as if users were losing information about their contacts.

“By default, messages from friends or friends of friends go into your Inbox. Everything else goes to your Other folder,” Facebook spokesperson Meredith Chin said in an email. “That is likely where the messages are being sent from other people’s emails. Even if that person is friends with them on Facebook, if the friend doesn’t have that email on their Facebook account, the message could end up in the Other folder.”

The problems first came to light on several blogs. Adobe employee Rachel Luxemburg, for example, noted that a co-worker had noticed his contact info for her had been updated with the @facebook.com address that was widely discussed early last week. But messages did not appear to be going through to her – perhaps, as Chin suggested, because they were being filed in the “Other” email folder.

“They’ve vanished into the ether,” Luxemburg wrote. “For all I know, I could be missing a lot more emails from friends, colleagues or family members, and never even know it.”

But the overwriting of contact information in people’s mobile devices may prove to be a bigger problem for Facebook. The company faced a backlash last week when it switched the default email address in people’s profiles to @facebook.com in an effort to jumpstart use of its email service, which has failed to live up to the “Gmail killer” status it was given when it first launched in 2010.

Facebook did not back down, but simply told users how they could switch their default contact info back to the email address of their choice. It was not clear if the fix for the updated contact info is a manual fix for each address in your device.

“Regarding the phone syncing issue, I’m having the engineers look into it and will get back to you as soon as I can with more details,” Chin said in an email early Monday morning.

dave copeland