merging the coverage from different testcase of the same DUT

Hi

     I am facing issue in the meging the code & functional coverage of the different testcase of the same dut

    commands used with iccr :

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set_dut_modules XYZ

merge test1 test2 -ouput temp

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following message is displayed : 

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Instance tree: txphy_top to txphy_top 

          "txphy_top.TESTCASE" to "txphy_top.TESTCASE": Control-oriented coverage not merged - Module name differs.

          "txphy_top.TESTCASE" to "txphy_top.TESTCASE": Block coverage not merged - Checksum differs.

        Items not merged:  2

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