The cause of this was several different bugs:

- When using binary logging with binlog_row_image=FULL
  the all bits in read_set was set, which caused a
  different (wrong) pattern for marking vcol_set.
- TABLE::mark_virtual_columns_for_write() didn't in all
  cases mark vcol_set with the vcol_field.
- TABLE::update_virtual_fields() has to update all
  vcol fields on REPLACE if binary logging with FULL
  is used.
- VCOL_UPDATE_INDEXED should update all vcol fields part
  of an index that was not updated by VCOL_UPDATE_FOR_READ
- max_row_length() calculated length of NULL and not
  used fields. This didn't cause any crash, but used
  more memory than needed.