I don't think it's a bug. I think that Finale is doing what it's supposed to do. But you may be right that this was different in earlier versions of Finale.According to the manual for F2K2b, the File menu's "Print Parts..." command doesn't allow you to make separate layouts for the parts:
"If you choose this command, Finale extracts the parts from your score by sending each directly to the printer. You won't have a chance to reformat each part before it prints; you won't even see it."
You mention that Finale 2002 "still offers the option of separate layouts for the parts and score". But I don't get that offer when I choose "Print Parts...".
When I choose "Print Parts..." in Finale 2002 I am sent directly to the printer driver's Print dialog box without first seeing any Finale dialog boxes that could allow me to specify a special scaling percentage for the parts.
On the other hand, both "Special Part Extraction" and "Extract Parts..." allow a layout different from the layout of the score.
For "Special Part Extraction" you can't save different scalings for parts and score, since they are in fact the same document. But you can print the parts with a different scaling. Just remember to return to the scaling for the score when you have finished printing the parts.
For "Extract Parts..." you can save both layouts, since they are located in different documents.
You can go to
Options menu > Document Settings > Page Format for Parts...
to save (in the score document) a different page format for the extracted parts.
Peter