I went to grab the patch that supposedly fixed the problem from https://github.com/mate-desktop/mate-panel/pull/845/commits/a130fb0379a270f6ed80fa21ba2a69e184b4cc2a and I find that has already been applied to the debian source. That fix adds conditional compilation for versions of GTK < 3.23, and sid is already on 3.24, so that fix would be irrelevant anyway. Is this a regression?