I finally found the explanation. Mea culpa, it was in the kerning in the font. All 3 lookup tables contained kerning -50 for small caps Cyrillic `t' and `a', and the was another one of -60 in kerning classes, which gave the total of -210.
I'm not sure if it is allowed and what should be the default behavior of typesetting program -- to add them of to use the last. If it is stated somewhere and you can point me to it, i will complain to my font vendor. And of course I will check for such cases myself and wipe out extra kerning. Peter and Vladimir, thank you for your help and patience. Vadim -------------------------------------------------- Subscriptions, Archive, and List information, etc.: http://tug.org/mailman/listinfo/xetex
