[plt-scheme] problem w/ namespace-require

The following code produces #t when run at the (module-language) prompt.

(begin
    (namespace-require '(prefix foo: mzscheme))
    (namespace-require 'mzscheme)
    (display (module-identifier=? (syntax +) (syntax foo:+))))

But the following module, when run in the module language, prints #f:

(module foo mzscheme
    (begin
    (namespace-require '(prefix foo: mzscheme))
    (namespace-require 'mzscheme)
    (display (module-identifier=? (syntax +) (syntax foo:+)))))

Why are these different, and what do I need to do to get the second to
produce #t?

sam th