The problem in 4.1 was the same as in 4.0 - fix_fields() not called for created Item_ref. 
The fix is similar too - initialize Item_refs in ctor (but don't interfere with cases when 
Item_ref is used by subselects). 


sql/item.cc:
  Fix for BUG#6976 ported from 4.0
sql/item_cmpfunc.cc:
  Fix for BUG#6976 ported from 4.0
sql/item_func.cc:
  Fix for BUG#6976 ported from 4.0
sql/item_row.cc:
  Fix for BUG#6976 ported from 4.0
sql/item_strfunc.cc:
  Fix for BUG#6976 ported from 4.0