GHI Values differ with module change

[J-L.Meier]

Der PVsyst team,

I performed 2 different simulations:

1) With 330 Wp modules

2) With 325 Wp modules

There was not changed anything else, except for the module type.

and noticed surprisingly, that the GHI values where different, what does not appear logical for me.

1) 1142.5 kWh/m²

2) 1141.1 kWh/m²

Is this a bug or is there a physical explanation for this?