I know this was discussed quite a bit atleast a year or more ago on lactnet.
Had a mom call today (baby is 9 months) and she tossed out frozen milk that
was only a month old.  It was kept in an upright refrigerator freezer.  She
used bags and never had this problem before.  The fat content did not mix well
when thawed and smelled bad as well as tasted bad.  I remember hearing that
the latex bags can do this and may also occur when there is a high fat
content.  She hasn't tested more recent milk that has been stored.  Any info
would be appreciated.
Sharon