PDF from 9.0 results in weird inter- and intra-word spacing. Cause?

Running Framemaker Version 9.0p250 on Windows XP.

I printed a book using the Adobe PDF printer driver. There are scattered instances where there are significant spaces (between 3 and 12 n-spaces) between consecutive letters of a word or between two words. For example:

Inter-word spacing examples:      main    processes employed and          the functional

Intra-word spacing examples:      audi         t         Descrip                        tion

These spaces do not exist in the Framemaker source files. In addition, when I copy the content containing these spaces to the Clipboard and then paste them into this message, the odd spacing disappears. However, when I print the pages containing these errors to my local or network printers, the pages print with the strange spacing intact.

I checked maker.ini and the setting is "DisplayUsingPrinterMetrics=On" as expected.

Any help much appreciated!

Val