I then asked this group who was right: munpack or the software which encoded
the body part with quoted-printable. The consensus is that the q-p software
is right and munpack is wrong.
We've had to advise the customer to stop using munpack because of this. (We
may even have to put out a general customer advisory on this issue.)
I agree, albeit reluctantly, with this assessment. Speaking as someone with a
MIME implementation that might very well elect to use Q-P for non-text data
should it prove to be more efficient, I'm going to have to consider pointing
people at a minimal MIME agent other than MUNPACK in the future.