The strange behaviour has led to a flurry of worries about the fact that the camera could be secretly recording people as they use the app. Unlike on Apple's computers there is no indicator when an app is accessing the camera, so it is possible for an app to do so in secret.
Facebook says the strange behaviour is caused by a bug that was added to the code by accident and that there is no indication that photos or videos are being sent to its servers. The company claims an update has already been submitted to Apple that should remove it.
In the meantime, the potential security flaw can be avoided by a simple fix in the iPhone settings that keeps Facebook from seeing the camera at all.
The bug first came to light after users noted that the app would occasionally shift the entire feed over to the right, as part of what appeared to be a bug. Underneath that main app a different screen could be seen – which showed video from the phone's built-in camera.
Facebook said that it had introduced the behaviour as part of an attempt to fix a different bug.
"We recently discovered that version 244 of the Facebook iOS app would incorrectly launch in landscape mode," a Facebook spokesperson said. "In fixing that issue last week in v246 (launched on 8 November) we inadvertently introduced a bug that caused the app to partially navigate to the camera screen adjacent to News Feed when users tapped on photos.
"We have seen no evidence of photos or videos being uploaded due to this bug. We’re submitting the fix for this to Apple today."
In a series of tweets, Facebook's vice president of integrity Guy Rosen said once more that content was not being stored in the app or sent to Facebook, and that it would be fixed soon.
“Triggering this bug activated the camera preview, and once triggered, the preview remained active until you tapped elsewhere in the app. At no point was the preview content stored by the app or uploaded to our servers," he wrote.
"We've confirmed that we didn't upload anything to FB due to this bug and that the camera didn’t capture anything since it was in preview mode. We’ve submitted a fixed version to the App Store which is already rolling out."
The problem can be fixed in the meantime by revoking Facebook's access to the camera. That is done by heading into the Settings app and navigating to the Facebook option – clicking that should bring up a number of permissions that have been granted to the app, including the ability to access the camera, which can be turned off by changing the toggle.
That will also mean that Facebook is no longer able to access the camera for more legitimate functions or features, such as the ability to capture and upload a picture straight from the app.