Hello Kirk,
I think that it must be something in the way PM5 records the caption:
The caption is visible in the IPTC Core in Adobe Bridge CS6 (5.0.1.21),
BUT
not in ACDSee 2 (2.2.172) Pro: the IPTC caption fields that are filled in PM5 are empty (in IPTC Core, IPTC IIM (Legacy) and in IPTC Extended Headline and Keywords are ok though)...
and not in Aperture 3 (3.4.3), that does not sees the caption, but sees headlin and keywords.
Photomechanic used to be perfect for my workflow, and still it is to classify and manage my pictures, however I cannot recover any picture based on its caption if I am not using Bridge! I would rather stick to PM5 for all of my filing and retreiving needs!
Looking forward to hearing from you,
Giorgio