Sounds like the user exists but doesn't show up in your list of users (or you didn't see him/her). Check again to make sure it isn't there already.
If not, make a check on the database integrety (there is an option for that) and see what happens.
If it is really a bug ti might have been solved long ago, because your installation hasn't been updated for almost a year. So before creating a bug report, update to the latest version and then see if the problem still exists.
I answer at the LimeSurvey forum in my spare time, I'm not a LimeSurvey GmbH employee.
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