I agree that they should work the same, but in this case, there is a discrepency.
in reply to Re^2: Using DateTime together with Template::Toolkit
in thread Using DateTime together with Template::Toolkit
I only suggested using the XS Stash instead since it seems to work correctly. Also, that message was posted to the TT mailing list a few months ago (in response to a message from the maintainer, so he's obviously aware of it) and there hasn't been a release containing the fix yet. That makes me think that waiting for the pure Perl Stash to work may take a while.