Unreported Change in Reverse Transposition Algorithm PVsyst v6.7.8 to v6.7.9

[kjs55]

There is a >0.25% difference in GHI when importing the same GPI data set between PVsyst versions 6.7.8 and 6.7.9. The release notes do not mention any changes to the (Hay) reverse transposition algorithm. The impact on annual energy can be >0.5%. Any ideas of what is behind this change? (NB: PVsyst refers to reverse transposition as "retro-transposition" or "inverse transposition".)