@MAG79
I don't think it's the case, because it happens always, no matter if the source is a film from a PAL DVD, a file, a video, and so on.
@Chainik
The data on madVR OSD confirmes what the data on SVP OSD says about the frame rate (i.e. a 23.976fps or 29.970fps file played at 59.940 and a 25.000fps file played at 50.000fps), and the resolution of the input file scaled at the display resolution, so I assumed that everything works fine.
The dubs came out when doing the setting of my system (i.e deciding where to do deinterlacing - LAV or madVR, if in film or video mode, etc.): I used the pin infos, and I started to wonder why the FFDShow OUT pin info always showed the orizontal resolution in multiplier of 1024 and never the incremented frame rate...
And it really drived me crazy trying to understand where and what caused the resize: it seemed like that the script used in Avisynth changed both frame rate and resolution, but I wasn't able to find it, neither in the FFDShow settings!!!