I have never heard anything like that ever happening.
I have in fact, created an user, and switched to it and just have kept it idle for the last 10 mins, without it logging me out.
Another user-switch you do on a daily basis: the simple "su" (which switches to super-user). I have never had an instance where the root logs out automatically after 10 or 15 or as a matter-of-fact, ever.
Can you please su to root and post the results?
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Thanks and regards,
Bodhisatta Barman Roy
International Institute of Information Technology
Bangalore