Thanks X10,
juddery or joggle may be a better word to describe the "problem" .
What I noticed is that, at first test run, tween have some interuption, almost always between about 50% - 80% of tween duration and juddery is constant.
If I run test again (ctrl + Enter), interuption is gone but juddery is still constant.
Maybe the problem is my graphics card. My CPU is Intel Quad Core, but I belive that graphic card (Ati Radeon HD 3850) is not so rubbish (or maybe it is ).
I tested swf on my wife's laptop and the situation is slightly better -
when I open swf with Firefox, at first run I can notice some small interuption and juddery is still here,
but again, if I do refresh on Firefox, tween is much smoother, I can say that interpution does not exist, and of course - juddery exist.