Why Does the Field Get Unexpectedly Deleted?

I have made a GUI in GUIDE. When myfun1 gets executed inside myfun2, suddenly field A gets deleted from variable handles.

WHY? What is the solution?

function myfun1(hObject, eventdata, handles)
handles.A = 1;
guidata(hObject, handles);
end

function myfun2(hObject, eventdata, handles)
myfun1(hObject, eventdata, handles);
end