Hmm, are you editing a JPEG after keywording and saving as a JPEG again?
I use PSP as well. I edit it TIFF, then save the final file in JPEG. With Exifer I can copy IPTC data from one file to another, so it's easy to deal with a series of images. The only problem with Exifer is when I want to include a keyword in a specific position for relevance, as Exifer only adds to the end of the list. That's when I use Irfanview.