Why sometimes the categorical come back to their original value in the table app designer?

I'm using a categorical value, first is calculated and expressed as A,B,C,D,E but when I want to change to do a recalculation sometimes come back to the previous value, and sometimes allow me to edit it

 app.T1.Data.extent = categorical(cellstr(app.T1.Data.extent), {'A', 'B', 'C', 'D', 'E'});

in the recalculation I'm talking the value as follow

         T1_1 = app.T1.Data;

sometimes allow me to change it, and sometimes not, show I created a callback for all the tables? My recalculation call a function and I tought it won't be necesarry to do so