You are using Case Merge Premium and noticed that a comment from the child case was copied twice onto the parent case after a merge operation.

 

During a merge operation, there could be two potential settings affecting how Case Comments appear on the primary case. 

 

The first is the setting for the Case Comment object within the Child Objects Tab in Case Merge Premium Setup. This determines if the Case Comment(s) will be cloned from the child to the parent and if the original Case Comment(s) on the child object should be deleted. 

 

The second setting,  Duplicate Case Description(s), determines if the Description associated with the Child Case(s) will be copied.

As the first step in troubleshooting this, please compare the content of the duplicate comments. If one of them includes the text "Description merged from case#", this means that the Description was merged as a comment due to the configuration of the "Duplicate Case Description(s) setting". Please note, even if you are performing a "Clean Merge", this setting will still be respected and Case Comment(s) will be created if that option is selected. 

If you wish to adjust how case descriptions from the Child Case(s) are merged, please visit the Case Merge Premium Setup and select an option from the dropdown.

 

Second, check the Child Objects tab in the Case Merge Premium Setup. If "Clone" is checked, the case comment will be cloned from the child to the primary case. If you do not wish for the object to be cloned, uncheck the box.