The IBM General Decimal Arithmetic Specification, on which the decimal 
module is based, has recently been updated to version 1.68;  the 
testcases from IBM have also been updated.

The comments in the decimal module clearly state that the decimal module 
should be kept in sync with the IBM specification, and that deviation 
from the spec is considered a bug.  So it seems to me that the decimal 
module should be updated, preferably before 2.6 and 3.0 come out.

As far as I can tell the required changes should be minimal:  max-
magnitude and min-magnitude definitely need changing, and there may be 
other minor changes necessary to make the new tests pass; I haven't 
looked properly yet.  I'll try to get to this in the next few days.