I am having the same issue this week. Initially it was just messages with my girlfriend, and was just an annoyance.
The problem has escalated today where it has created a group with my girlfriend and one of our contractors. So now if I send a message to just my girlfriend, it will remove the message from that chat, and add it to the chat it created with my girlfriend and the contractor, and the same if I send a message to the contractor.
This has made Link to Windows/Phone link unusable until this problem is acknowledged and resolved.