Well, tried changing timeout in screen settings and the same thing happened. It did not timeout on its own but in time specified in settings.
Since I hate having two apps for same thing I was reluctant installing aldiko. Anyway, I tried it and the same thing happened, only this time display did not dim before turning off and after turning it on it was not locked (strange).
So, I create new profile (manually) by increasing timeout before I start reading; 10 mins would be enough time for me to read two pages before display turns off, and as my reading skills progress I might reduce it to 5mins as more permanent solution
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Than you for suggestions.