Why is this?
1) The originator makes the error.
2) The first part expires before the second part is posted.
3) A site policy is to expire 1/n parts to discourage use of multipart
postings.
I it is 3), the program that expires the 1/n message is brain dead or
the administrator doesn't know how to write a simple perl script. I can
see expiring 1/n where n is large, but most images are two or three
parts only.
In any case this is a serious admin bug on this site.