Sometimes you want to su as some person and usually you know his/her name. Some people have multiple accounts with some of them being inactive and you don't know which are active and which aren't. So you just pick random one and... if you have tried to su as an inactive user, you will be logged out (I also got redirection loop sometime, when trying to su on some admin pages). There's no message about what happened.
1) There should be no redirection loops
2) You should get an error that chosen user is inactive (or even exclude him/her from search result). After getting an error, you should still be logged in as you.
Bug
Closed
Trivial
