The value of the Decimal hash() depends on the current context:

>>> from decimal import *
>>> x = Decimal("123456789.1")
>>> hash(x)
1989332493
>>> getcontext().prec = 6
>>> hash(x)
-2034270682

This has nasty consequences;  e.g.:

>>> s = set([x])
>>> x in s
True
>>> getcontext().prec = 28
>>> x in s
False

hashing a Decimal can also set flags in the context;  again, I think
this is undesirable.

The cause of this bug is clear:  __hash__ calls normalize, which rounds
its argument to the current context.  I'll post a fix when I get around
to it.