As in Excel, dates in EasyMorph are numbers, formatted as dates. Such numbers represent a number of days since January 1st, 1900. For instance number 42680 corresponds to November 6th, 2016, because there are 42680 days from January 1st, 1900 to that date.
Therefore, adding 1 day is just adding 1. For instance:
It seems that you are adding 1095 to zero. Can you please send an example project, which replicates the problem, to our support email so we can check it out?