Statgrphics Question

#1
I ran an ARIMA (1,1,0) + constant model in Statgraphics. It reported back a constant plus a mean plus the rest of the ARIMA model. When I checked on the forecasts of the model by hand calculation I found that Statgraphics ignored the mean when doing forecasts. Why? Statgraphics claims that it's basing the forecast on ARIMA (1,1,0) + constant. Does this imply that it ignores the reported mean?

Thanks

Mark