One of the fixes in the 1.23 firmware is it makes the wattage needle in the P15 display correctly. see, P15/P20 1.23 Firmware Live!
I do not recall any discussion that 1.23 is scaled improperly for the P15, but I may have forgotten. Cite?
By the way, luigi61 is referring to 1.25, not 1.23. His post is the first mentioning a power meter scaling issue with a P15 running 1.25. @jamesh are you aware of a power meter display issue with 1.25?
Luigi61, there is no problem reloading 1.23 if you would like to do so.