This is a follow-up to this post: http://community.logos.com/forums/t/55708.aspx
First repeatable bug: When building a new PB for the first time, fields in the book are not recognizes (or at least, they don't show up in the information panel).
Create a new personal book using the Add Book button in PB panel.
Add a file that contains field codes and compile it. This is the text I used in my .docx file:
{{field-on:words-of-christ}}Words
of Christ{{field-off:words-of-christ}}
{{field-on:season}}Church
Season{{field-off:season}}
{{field-on:date}}Calendar Date{{field-off:date}}
{{field-on:day}}Lectionary Day{{field-off:day}}
{{field-on:year}}Lectionary Year{{field-off:year}}
{{field-on:heading}}Heading{{field-off:heading}}
Look at the information panel of the new book.
The Search Fields section is empty:

In the personal books panel, rebuild the book.
Now the information panel looks like this:

Second Problem: When compiling a PB that uses both Word Heading styles and {{field-on/off}} tags to mark the same line of text, the compiler does not recognize the fields correctly.
To test this, I used three example files.
Create and compile a file with the following text: (MAKE SURE TO BUILD IT TWICE, because of the above-mentioned bug)
{{field-on:date}}
Sunday, December 2, 2012
{{field-off:date}}
{{field-on:season}}ADVENT{{field-off:season}}
{{field-on:day}}
First Sunday of Advent
{{field-off:day}}
This file works correctly. It compiles without errors or warnings and the information panel looks like this:

Now, create and compile a file with the following text. Use Word's Heading 2 for the date and Heading 3 for the day (you can actually use any word style to get the same behavior)
{{field-on:date}}
Sunday, December 2, 2012
{{field-off:date}}
{{field-on:season}}ADVENT{{field-off:season}}
{{field-on:day}}
First Sunday of Advent
{{field-off:day}}
Note that the text is exactly the same as the first file, except for adding the word heading styles.
But when the PB is built, the log contains the following warnings:
[Warning] closing field date
that is already closed.
[Warning] closing field day
that is already closed.
This should not create a warning... the heading field/style was closed but the date & day fields should not have been closed! More troubling, is the information panel:

Note that Calendar Date and Liturgical Day are missing.
Now, remove the field-off tags for Date and Day so that the file looks like this:
{{field-on:date}}
Sunday, December 2, 2012
{{field-on:season}}ADVENT{{field-off:season}}
{{field-on:day}}
First Sunday of Advent
This file compiles without any errors or warnings, even though the {{field-off:}} tags are missing. There should be a compiler warning here!
The information panel looks the same as the second example... the Calendar Date and Liturgical Day fields are not recognized.
At this point, we might expect to see the text {{field-on:date}} and {{field-on:day}} in the PB since the compiler apparently didn't recognize them, but the body of the book looks like everything worked perfectly.

My guess would be that the compiler recognizes and accepts the {{field-on:date}} code and then recognizes the Word Heading Style. When the heading style ends, the compiler closes all open fields instead of just the heading style.
Whatever the problem is exactly, something is wierd!