San Francisco, Oct 1 (IANS): An issue in the "unified thread" functionality for iMessage that comes as part of Apple's iOS 12 update is merging threads with different contacts and sending messages to several people unintentionally, the media reported.

The "unified thread" feature creates multiple chat threads for a single contact in situations where a contact switches SIM, uses multiple Apple devices or uses both email and phone number to chat on iMessage.

The problem is being reported by a significant number of iMessage users ever since the update started rolling out, and of late, the number of complaints have swelled up, PiunikaWeb reported on Sunday.

"To get a message to the intended recipient, I create a new message with the correct contact. Once the message is sent, it joins up with the combined message thread," a user added to the complaints flooding Apple's Support page.

Majority of users facing this issue share a common "Apple ID" with some of their family members, which may lead to speculation that the new streamlining feature in iMessage treats Apple ID as the basis for merging/combining threads, the report added.

Apple rolled out the latest version of its operating system (OS) -- iOS 12 -- earlier in September, promising to bring performance improvements across the system with features like faster camera and keyboard launch, "Screen Time" to track the amount of time users spent interacting with their devices and "Siri Shortcuts" that allows any app to work with Apple's digital assistant Siri.