Forwarded Email getting associated with same Case

I have noticed that forwarded email from a different sender for an existing case, if there 

Explaining the Scenario:

1. I have configured a mailbox and Queue for email address say: dymmy@mycompanydomain.com

2. Case Creation rule is configured for any email coming to this queue.

Sending Emails in 2 different scenarios:

1. Sent email from ABC@outlook.com
   1. TO :  DEF@outlook.com & XYZ@outlook.com
   2. "Replied to All" from DEF@outlook.com to ABD@outlook.com, XYZ@outlook.com and Added dymmy@mycompanydomain.com email address as well.

                                                     i.     New Ticket got created in dymmy@mycompanydomain.com queue.

1. 1. "Replied" to All from XYZ to ABD, DEF and Added dymmy@mycompanydomain.com mailbox as well.

                                                     i.     New Ticket got created in dymmy@mycompanydomain.com queue. – Working as expected.

1. Sent email from ABC@outlook.com
   1. TO :  DEF@outlook.com & XYZ@outlook.com
   2. Replied to All from DEF to ABD@outlook.com, XYZ@outlook.com and Added dymmy@mycompanydomain.com email address as well.

                                                     i.     New Ticket got created in dymmy@mycompanydomain.com queue.

1. 1. Forwarded from XYZ to dymmy@mycompanydomain.com mailbox.

                                                     i.     Incoming Email got associated with existing Ticket in dymmy@mycompanydomain.com queue.