Set focus on a input text field but can not input anything!

1, when i close a child window with grid in it,and call destructor method of the grid in the window,i can set focus on a input text field in the parent window which also has a grid in it, but i can not input anything with focus on the input text field; in order to input text i must first select a gird row in the prarent window ,it seems once i select the row it will unclock the keyboard!!!
2, and when i close the child window ,and do not call destructor method of the grid in the child vwindow,i can set focus on a input text field in the parent window and i can input anything with focus on.
3,same thing is occurred when i close a tabbar and call destructor method of the grid in the tabbar ,when the focus is set in the next tabbar content , i can not input anything with focus on

Please attach completed sample that allows to reproduce the problem:

docs.dhtmlx.com/doku.php?id=othe … leted_demo

because my code is too large and complex ,so i will try to deliver a simple example which can reproduce the problem this weekend.
i also have find some clue which may be useful:
i find it that there is a which store a avtive dhtmlxgrid object,when active dhtmlxgrid object call destructor method , the is set to null,and method can not continue,so the input field in the web page and input field in dhtmlxtoolbar can not input anything ;
and at this moment when we select some row of another grid in the web page or when we call selectrow method ,the will be set some value ,and then we can input thr keyboard !