Same .m file: different results with different versions of Octave

[Perseu]

I am trying to fit some data with a function of a complex variable.
The same .m file gives me different results in different versions 
of Octave.

Versions 3.0.0 (Ubuntu 8.04), 3.0.1 (Debian Lenny), 
3.2.3 (Salix 13), and 3.2.4 (compiled on Debian Lenny) give result A.
Versions 2.1.7 (Debian Etch) and 3.2.3 (Windows XP) give result B.

Only the result B is correct when compared with Mathematica 7.0 (Wolfram).

All my systems are 32 bits and I use official binary versions 
(from Linux distro repositories).

This is a normal Octave behavior?
What can I do to solve the problem?