Null j2-stripes when Q2>1 in 1d ?

[lostanlen]

Hello,
I don't understand the following behaviour of the 2nd-order scattering in 1d. Some coefficients are exactly zero when Q2>1 and j2<j1, even when path_margin == Inf. At first, I thought it was because the anti-aliasing filter (named lowpass) in conv_sub_1d doesn't intersect the range of values 'rng', but the same problem happens when filt_opt.format is 'fourier_multires' or 'fourier'.

Below is a minimal working example. Oddly enough, setting filt_opt.B = [8 1] seems to solve the problem ; why so ?

N = 32768;
load handel;
y = y(1:N);
T = 4096;
filt_opt.Q = [8 2];
%filt_opt.B = [8 1];
filt_opt.J = T_to_J(T,filt_opt);
filt_opt.format = 'fourier';
scat_opt.M = 2;
scat_opt.path_margin = Inf;
[Wop, filters] = wavelet_factory_1d(N, filt_opt, scat_opt);
[S,U] = scat(y, Wop);

set(figure(1),'WindowStyle','docked');
[~,sc2] = display_slice(S,1);
imagesc(log(abs(sc2)); % display energy in log-scale to see the black vertical stripes
figure(1);hold on;colormap copper;hold off;drawnow;commandwindow;