Hi,
Your MIRO document posted on 15.03.2016. As your MIRO posted with excise tax code where excise tax code contain excise tax components.
Now check tax rate for excise tax code on 15.03.2016 and now what is tax rate for your excise tax code on the date for which you are cancelling your invoice document.
Cross check may be different tax rates for March month-2016 and April month-2016 for excise tax code(FV11) with excise tax condition types which causing your concern!
Regards,
Biju K