Oh noes… it’s indeed GTK+3 build 
Just checked https://launchpadlibrarian.net/283298574/libmateweather_1.14.1-1~xenial1.1_1.14.3-1~xenial1.0.diff.gz and it’s indeed built with GTK+3. That’s a sure crash when using the library in GTK+2 apps.
3 Likes