Duplicate Chat-Windows

Hello everybody,

we're using GroupWise Messenger 18.0.1 on a OES2018 and determine several users with the following problem:

Chat-windows getting opened twice/duplicate for the same chat - sometimes only if the other user closes chat-window and starts a new chat with me (so I have two chats with same user) - but also sometimes two chat windows are opened with the chat initailisation (first and same message).

Ist there a known problem or does anybody have an idea how to get this problem located or solved?