There's a difference. In Spanish, when you use "mismo/a" after the subject, you're refering to his/her/itself. But if you use "mismo/a" before the subject, you're talking about "the same". Here's an example:

La misma sopa = The same soup, as "I have the same soup as my brother". La sopa misma = The soup itself, as "we were warmed up by the soup itself".

Looks like "misma" always precedes the noun it modifies. So "la sopa misma" is simply a mistake, rather than having a different meaning.

Certain verbs always come before the noun in Spanish (mismo) and can having different meanings depending on placement (grande/gran). http://spanish.about.com/cs/grammar/a/whereadjective.htm

It seems to be a tricky word with different uses! According to AboutSpanish as well as its use here as an adjective, before the the noun, it can be used before or after the noun to give emphasis and it is used after a pronoun, to give '-self' see http://spanish.about.com/od/adjectives/a/mismo.htm

el mismo caldo = the same broth

Guess it's because they're using Spanish Spanish, not Mexican Spanish?

I think when feminine agreement is always necessary.

a feminine noun goes with a feminine adjective most of the times, if not all :)

"mismo" is an adjective, adjectives must match the nouns that they describe in number and in gender. http://www.studyspanish.com/lessons/adj1.htm

"mismo" is one of those adjectives that typically goes before the noun. http://spanish.about.com/od/adjectives/a/mismo.htm

No. "Soap" is "jabón" in Spanish. http://www.wordreference.com/es/translation.asp?tranword=soap

http://www.studyspanish.com/lessons/defart1.htm