There were two problems that caused wrong results reported with this bug.
1. In some cases stored(persistent) virtual columns were not marked
in the write_set and in the vcol_set bitmaps.
2. If the list of fields in an insert command was empty then the values of
the stored virtual columns were set to default.

To fix the first problem the function st_table::mark_virtual_columns_for_write
was modified. Now the function has a parameter that says whether the virtual 
columns are to be marked for insert or for update.  
To fix the second problem a special handling of empty insert lists is
added in the function fill_record().