[Gretl-users] ARIMA v. OLS seasonal difference

Is there any obvious reason why using the ARIMA feature (without any AR or MA terms) with a seasonal difference=1 would yield different coefficients that using OLS and manually seasonally differencing the independent and dependent variables? I am using monthly data. I like the ability to difference the data within ARIMA because it automatically un-differences the data when producing forecast and residual results. Any assistance anyone could provide would be appreciated.