Actually I spoke too soon. After rebuilding oct2mat as above and
restarting Octave, I can do the following commands and get a figure
window that responds as expected:
figure;
x=[1 2 3 4 5 6];
plot(sin(x));
However, another (much more complex) figure that I produce (in the same
Octave session) is not responsive (ie, no ability to zoom, displayed
coordinates do not track mouse movements).
I will try to narrow down the cause of this difference in behaviour...
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It turns out that using imshow() to display an image is what is causing
the figure window to freeze. I drilled down into the source code to see
if I could find the ultimate cause: