Some users said that when they viewed a video in full screen and then shrank it back, the app layout would shift slightly to the right. In the space on the left, you could see the phone's camera had been activated. CNET says it was able to replicate the issue.

Today, while watching a video on @facebook, I rotated to landscape and could see the Facebook/Instagram Story UI for a split second. When rotating back to portrait, the Story camera/UI opened entirely. A little worrying... pic.twitter.com/7lVHHGedGf — Neo QA (@neo_qa) November 2, 2019

Facebook says the bug was introduced when it fixed another issue -- the Facebook iOS app incorrectly launching in landscape mode -- in version 244. "We have seen no evidence of photos or video being uploaded due to this bug," a spokesperson told Engadget.

We recently discovered our iOS app incorrectly launched in landscape. In fixing that last week in v246 we inadvertently introduced a bug where the app partially navigates to the camera screen when a photo is tapped. We have no evidence of photos/videos uploaded due to this. — Guy Rosen (@guyro) November 12, 2019

Needless to say, this doesn't help Facebook's image. The company has doubled down on its messages about privacy and security, and a bug like this could undermine the company's efforts to improve its reputation.

Facebook's full statement is below: