After it is published on the interface the server waits for one client to acknowledge the reception of the message. Usually such an acknowledgement is automatically generated by a client PLC reading the information.
If a message requiring an acknowledgement has been published it will stay active till an acknowledgement has been received, even if the cause triggering this message has already been cleared.
As a Reset method call tries to bring the system back to an initial state it clears all active messages. If an error state could not be cleared the message will show up again after performing the reset.