[ZPT] path() changed in tales?

[alex]

I have the following expression:
tal:define="offset python:path('request/offset') or 0"

and receive the following error:
Error Type: Undefined
Error Value: offset not found in 'request/offset', at line 133, column 1

it used to work on my previous zope installation Zope 2.4.1 (binary release,
python 2.1, win32-x86), python 2.1.0, win32

it fails on my new zope Zope Version    (Zope 2.5.0 (binary release, python
2.1, win32-x86), python 2.1.2, win32)

why isn't zpt backwards compatible?
or maybe it's a general zope or even python problem.. but it used to work,
and still does on previous release.

any ideas?

Alex