Editable Column--new value disappears and shows default val after hitting enter

I have a column editor whos value is defaulted to the value from another column. Once you edit the default value and click enter, it shows the dirty red flag on the cell but also the default value, instead of the new edited value. To see edited value user would have to dbl click that cell again--re-enabling editor.

Its that how it is? Or is it because I ve set a default value on that column?

to set default val on editable column, ColumnC, I added a renderer:

colCRenderer: function(val, meta, rec){

return rec.get("ColumnA");

}

thanks