Counterfactual after fixed effect estimation (pb with xbu option)

Hi,

I can't find my way around the behaviour of the xbu option when trying to compute a counterfactual.

I run an estimation with fixed effects like this

xi: xtreg lexports $regressors fe1 fe2, fe cluster(pairid)

then computed the prediction of the model, fixed effects included

predict lexportmodel, xbu

then I modify some regressors but only for years after a cut off date
and finally I use predict again to built a counterfactual.

predict lcounterfactual, xbu

My problem is; with the option xbu, the counterfactual is different from the first prediction of the model before the cut off year. Without this option it's ok (both the prediction and counterfactual are equal before the cut off date).
So it seems to me there is something peculiar with xbu.

Does anyone know why there is this issue with the xbu option ?
And do you have a solution ?

best,
Aurélien