Power enchantment level above 255 has no actual effect

If one uses command to create a bow with power level above 255, for example, {lvl:15000s,id:"power"}, and then uses this bow with "Power enchantment.level.15000" to fire an arrow, the "damage" NBT of the arrow would be 130.0d(corresponding to power level 255) but not (2.5 + 15000 * 0.5) = 7502.5d (corresponding to power level 15000).