When you press the Enter key on the keyboard to sign in Outlook Web App in a Microsoft Exchange Server 2013 environment, the sign-in form is submitted two times. This may cause unnecessary memory consumption on the Client Access server.
This issue occurs because it is a designed function in Exchange script.
To resolve this issue, install the following cumulative update:
2961810 Cumulative Update 6 for Exchange Server 2013
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.