In a Views page with 3 arguments, 3rd argument default PHP being ignored if 2nd argument is not present Using Views 2, I have a View with 3 different vocabularies as arguments.

The first 2 are intended to be acquired from the URL, however the 3rd will only ever receive it's value from the Default Value PHP Code. 

However if argument 2, which is optional, is not supplied, then Argument 3 is not evaluated.

SOLUTION:

Just to clarify where I landed:

The default option Action to take if argument is not present is always set to something (there is no do nothing). 

It was already set to Display all values which was not working. 

However Provide default argument > Fixed Entry > "all" while the argument wildcard is also "all" is allowing the 3rd argument to be evaluated.
Always keep the optional args in the end otherwise define Action to take if argument is not present or at least set Provide default argument in argument configuration form.