Hello,
sorry for the delay I was on holiday. I tried it in two different themes and in both it works and pictures change size right.
1 theme: http://prntscr.com/Q0Eowv3emJQz
2 theme: http://prntscr.com/w_M9tBOHsFKg
I use this themes: http://prntscr.com/K7OHsOT0jzAO

So it really looks that it is theme problem.
Thank you for your response.
Katerina