I am currently using SonarQube CE7.9.1 and have five users added (using the build in security). However I can only see three of them. Looking in the database, tbl.users I can see the five entries and they look similar in that all fields are basically entered and look the same.
I cannot reproduce your error. I tried with a fresh install of a CE 7.9.1, created 5 test users, and I can see all of them. The footer correctly shows “6 of 6 shown”: