Successfully reproduced with Tomcat, JBoss and Glasfish

Create new group with group ID that contains at least one backslash "\"
The goup cannot be edited --> "Communication Error: The application received an unexpected 400 response from the server. Try to refresh the page or login and out of the application."
The group cannot be added to a user --> "Communication Error: The application received an unexpected 400 response from the server. Try to refresh the page or login and out of the application."