"Copy price set" does not copy the Percentage Price Fields properly -- they're copied as mere checkbox fields, where the single checkbox has the label "ERROR: percentagepricesetfield_NFMbsQAQVpVZkamC (Hint: Is the Percentage Price Set Field extension enabled?)"
This appears in some newer versions of civicrm (not sure at what version this began happening) because of a minor change in the format of the auto-built value of civicrm_price_set.name on copied price sets.
"Copy price set" does not copy the Percentage Price Fields properly -- they're copied as mere checkbox fields, where the single checkbox has the label "ERROR: percentagepricesetfield_NFMbsQAQVpVZkamC (Hint: Is the Percentage Price Set Field extension enabled?)"
Example preview of copied price set: