When put rending gale charged on pedestal, the number of charged feathers will be multiplied by 100. Using a hopper can remove more feathers than the charged amount, thus duplicating feathers.

This is fixed in 1.21.1 and later releases. Unfortunately applying the same fix to 1.20.1 would require a lot of refactoring so I decided against fixing in there. Not sure where you're experiencing this, but I am closing given the fix is present in newer versions.