The lostfocus of the last control of the form you could set the focus to the first control on the form. This will override the default behaviour and eliminate the problem.

>But I have already built my application and I am in middle of debugging it
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>>>I got a problem. Whenever I press tab in the last object of child form in a formset (in respect of whatever mode I am i.e., edit or Add mode) it goes back to the top most form. I tried every thing like MODAL etc. but to the control goes back to top most form.
>>>Any suggestion would be highly appreciated.
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>>This is the expected behavious.
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>>Formsets are not usually worth the problems. Think about using 1 form with several pages on it.