File length of cut layers are larger than the original file

When I save a layer made by cuting an harmonic range, selected on all the original length file (32 float bits / 44100 Hz / stereo) it has a larger length.
An empty zone appears in the right zone.
It happens the same thing if I edit the layer in an external editor (soundforge in my case).
Does someone have an explanation (it’s about the latest spectralayers pro 8) ?
Thank you