matlab's GUI KeyPressFcn

I am using the KeyPressFcn method for the edit box to test whether enter is pressed. I can use call_back but there is not event_data call_back function.

If I press one time on the button of Enter, than text doesn't rewrite, but if I double time on the button of Enter (speedly), than text rewrite.

What reasons this behaviour?

   function WriteData(val, name, ind)
           global solver;
           switch ind
               case {14, 15}
                   value = strcat('@(t)', val);      
               case 16
                   value = strcat('@(x)', val);
               case {17, 18}
                   value = strcat('@(x,t)', val);
           end
           eval(strcat('solver.', name, ' = ', num2str(val) ) );

      function edit1_KeyPressFcn(hObject, eventdata, handles)
           val = get(hObject, 'String');
           [~, ~, var] = GetActiveData(handles.listbox1);
           ind = get(handles.listbox1, 'Value');
           if (strcmp(eventdata.Key, 'return') )
               WriteData(val, var, ind );
           end