Ned - you bet me to this post. The issue of the Post checkbox not remembering and being set on is a known issue and has already been resolved. Ned - I will close your issue as a duplicate and resolved.
In the meantime - you can script a fix:
Go to System -> Design -> Scripts and create a new script called
printMulticopyDocument (case sensitive)
In that script copy the following script (also case sensitive):
Save and the screen should default to the post checkbox being off.