Dear nitin,
The issue was once we assign a DMR to characteristics level, there's tick to "Used in task list" under Usage Indicator tab in t-code QDR2/3. i didn't knew it , so when I assigned a DMR to a material and went on to check the changes in that particular DMR, I saw that tick. Initially I thought that there's must be something at config level. But later i came to understand that when a DMR gets assigned at characteristics level, that indicator indicates that the DMR is now in use.
Apology for the wrong attachment earlier. Attached here is the correct one.
Regards,
Rahul.