Tab group disappears

I have some kind of login window, it's opening at the the start of app, also I have tab group with few wins on it. So when I push login button(that is placed on the login window) I close login window and open bar group. On one of the windows logout开发者_开发问答 button is placed, and when I click on it, tab group is closing and login window is opening. After few iterations of login\logout actions, bar group stops to open. What should I do?

It was Just because I didn't specified the size of the button