When accessing the (invalid) URL "default/admin/users", either because the URL is entered by hand, or because an overview page contains an incorrect link, an infinite loop is triggered, ultimately resulting in the servlet container going out of memory. According to the log, the request results in "internal/users" and "default/admin/sitetree/internal/users.xml" then (down the road) "internal/internal/users" and "default/admin/sitetree/internal/internal/user.xml" and so on.
Note: Gregor says, this will likely go away with the migration of the remaining admin usecases to uc fw. the problem seems to be in a view pipeline.
this has been fixed