[mod_python] merges results from previous requests of the same page

I'm getting some artifacts when I execute multiple time a script with
different parameters, under mod_python.

Basically I have a small applications which, depending of the value of
a GET variable, reads some files stored in the server and returns to
client a small web page, a representation of the values in those
files.

But the problem is that, when I request a page for the second time,
apache returns a page which mixes the results from the previous
requests of the same, even if it had different parameters.

Let's make an example.

http://localhost/samplescript.py?values=1
output: _|______

-- restart apache --

http://localhost/samplescript.py?values=2
output: ______|_

-- restart apache --

http://localhost/samplescript.py?values=1
output: _|______
http://localhost/samplescript.py?values=2
output: _|____|_


How is that? I though mod_python initializes a different
sub-interpreter every time a page is requested.
My configuration of mod_python is very basilar: I have not configured
any caching directive, and I am using a customized publisher handler.
I am on a Ubuntu (same problem on debian), mod_python 3.3.1-2build1 on
apache 2.2.8-1ubuntu0.2.