Matthew,
I'm using PM 4.6.1 on a Vista PC and some of the iptc fields I use are at time altered or missing...(This was noticed in Win XP aswell)
The Category field is often shortend from Sport -> Spo
The Credit field is shortened from Matthew Greenfield | Perth Sports Photography -> Matthew Greenfield | Perth Sports
The copyright field extra characters appear -> © 2009 Perth Sports Photography | All Rights Reserved
(extra character highlighted)
and the Copyright URL is often missing completely...
Question is ... what could be causing this and how do I rectify it??
You're likely using Photoshop after you've captioned your images. Photoshop is enforcing limits on the lengths of some of the IPTC fields (Category at three characters long). The additional character is happening because the copyright symbol isn't being interpreted correctly by Photoshop (it is interpreting the character encoding based on the encoding of your system instead of the encoding you've chosen in Photo Mechanic.)
What can be done? Use XMP only instead of IPTC. Or, do all of your image modification before you caption.
Photoshop insists on changing IPTC data even if the only thing you did in Photoshop was to edit the image data.
The Copyright URL is one of several fields that can only be represented in XMP. Make sure you're writing out IPTC4XMP for your images.
-Kirk