Updating a PO file with makemessages without removing previous translation strings

[Tim Langeman]

I'm having trouble appending new translation strings to an existing po
file without removing some of the previously translated strings.

Here's some background:
-------------------------------------
I have a project that I've divided into sections. I have removed some
templates from a section that I do no want to update for this
particular language, and I have updated other templates by marking
additional strings.

I had previously created a po with existing translations that total
857 strings (0 which are untranslated), but when I run makemessages,
it removes some of my strings, resulting in a smaller file of 603
strings (26 which are untranslated).

The documentation says that makemessages "creates (or updates) a
message file in the conf/locale (in the django tree) or locale (for
project and application) directory."
http://docs.djangoproject.com/en/dev/ref/django-admin/#makemessages

The syntax I am using is:
python manage.py makemessages -l es

Based upon my attempt, it does not appear as though the "update" is
happening as expected. Is there something I should be doing
differently, or is my interpretation of "update" wrong?

-Tim Langeman
Akron, PA (USA)