Kurt,
I had a problem selecting photo fields also, but not exactly the same as your's. I have a file geodatabase axf that was created in ArcPad 8. It uses a custom form for a layer with a related table, but I had to roll my own because related table forms were not availble then.
After installing ArcPad 10, I checked out the data again using the old ArcPad 8 axf as a template. There were fields to select and I did select them, but when I used the form the fields you could select on the Picture page were not limited to the ones I had picked!
I found out that there are new xml elements for this functionality: <PICTUREPAGE> AND <PICTUREFIELD>. I just added them to the xml for my layer inside my <EDITFORM> tags (see attached image). It works as it should now, although I have not tried a new check-out yet using this axf with the as a template.
-Jane