Octave's stacked option appears to work differently than Excel. I prefer Octave's behavior (although it would be considered a bug
if it differs from MATLAB, I don't have MATLAB to check).
Confirming that Octave's behavior is not matlab compatible. running both Olivier's and Tony's code in both octave 5.2.0 and Matlab 2020a, tony's code looks identical in each (except for colormap), Olivier's code in Matlab looks identical to Tony's (except the negative part is a different color), while Olivier's code in Octave has the negative bar overlapping the rest of the chart.
should probably be captured in a compatibility bug report. If a search doesn't turn up an existing one I'll file one with all of the images for comparison.