Back button : hitting back button not taking me to my last activity

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http://androidforums.com – in my application having two activities like , activity A as main and launcher, and activity B, scenario : activity A started after launching app. started activity B from A, started another activity X of other application from B. now hitting BACK button of hardware, taking me to the Activity A. it actually should go back to the activity B , as it is the last activity. it is working properly in android 2.3 but not in android 3.0 honey comb ( samsum tab 7´ is working fine and failing in xoom tab). it very urgent fix needed please help me . thanks and regards rafiq (General)