Looks like there is an issue when applying multiple templates where templates applied first affect those that are applied later.
For example,
I apply the zombie template to the base creature which removes all immunities, dr, etc. from base creature. Then I add a template that grands an additional immunity to the now zombie creature, but the zombie template still removes it.
As I understand stacking templates is that they apply in the order in which you place them.
For example,
I apply the zombie template to the base creature which removes all immunities, dr, etc. from base creature. Then I add a template that grands an additional immunity to the now zombie creature, but the zombie template still removes it.
As I understand stacking templates is that they apply in the order in which you place them.