I've found Debian bug #807424 [1] on a similar issue which was resolved by making kdenlive depend on oxygen-icon-theme. Probably, it's time to change this dependency to the Breeze icon set.
(The reason I suggested to add this dependency as Recommends is that kdenlive can use other icon themes as well, so Breeze is not strictly needed. The attached screenshot shows it using Oxygen icons, for example.) [1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=807424 -- Алексей Шилин
