Test Case is passed though Checkpoint doesn't match

Hi,

In keyword test case i have placed the check point (property checkpoint)  on error message. ("Error message A" )

E.g. 

If Drop down 1 --> XYZ  and Drop down 2--> ABC  then system displays error message "Error message A" 

when i change input values in key wordtest, so that error message does not display . In this case after running test system should have faild the testcase as  "Error message A"  is not getting displayed right...

But actually tescase passed successfully 

Can any one explain this?

Regards,

Bhakti

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