And I am still baffled about this bug. The more I look at the code, the more it looks OK. Of course I am not claiming what You are saying is not true, just have no idea what causes this bug.
Thanks for the info and sorry for Your inconvenience, I will take a look at it once again. BTW, when You see something like that, please send me print screen of the bugged scene - stats at the bottom included. It will greatly help me to find the bug (there is possibility that in occurs with some specific values).