CNBC tested the bug on Monday that lets you hear the audio of the person you are calling before they accept the call. The issue was first reported by the Apple-related website 9to5Mac.
The bug appears to fool a call recipient's phone into thinking a group call, which involves more than two people, has already started. It then switches the recipient's microphone on without them ever having to accept or reject the call.
Despite the temporary removal of the group service, users of FaceTime are still able to continue using the one-to-one FaceTime function.
A spokesperson for Apple told CNBC Monday that a fix is coming this week. "We're aware of this issue and we have identified a fix that will be released in a software update later this week."