Hi Arghya
I understand your concern....let's do one simulation. if you are doing this activity other then production system then please
1) Put the check mark back on Storage section check active in storage type and you will find instead of "Y" value will get changed to "X" ,
2) Change it manually to "Y" go back to master data . storage type and remove the check mark from "Storage section check active" and you will find that "Y" will disappear from the "Storage Section Check"
This make sure that the moment u make any change in storage type the value in "Storage Section Check" automatically change blank or "x"
Now the third test
Remove the check mark from "Storage section check active" and then manually put the value into "Storage Section Check" and you will find that system accepts the value without any warning / error (Standard SAP behavior)