Hi, I'm pretty sure we didn't backport the commit [1] to 1.18. This change was meant for 1.20, and we also made similar changes in Caja and Pluma (in Pluma it's in filebrowser plugin).
[1] https://github.com/mate-desktop/mate-panel/commit/e04356360b9277fa6001f57df712752b315d1be3
