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an alien who failed to maintain the previously accorded status or whose status expired before the application or petition was filed" .

This sentence sounds conflict.

-No. The point is "before the application or petition was filed" . If you filed the change of status application before your status expires or is invalid, your application would possibley be approved.

 Do I have to maintain the previous status untill  final petition decision was made

-Not have to.

or untill my petion was filed?

-Yes.

Thanks!