Myeah, messy, really messy. Certain gtk2 applications, in this case Deadbeef player in gtk2 mode will constantly reset the icons each time one changes a theme/color or iconset in ksettings. Now, that shouldn't be an issue as such were it not that the default Breeze icon set simply isn't complete. Personally I have Breeze, Breeze Rounded corners, A custom color script for both of those and the Chameleon set for both of those. None, since they're based on default Breeze or Breeze RC contain all needed icons. That is, Breeze RC even has a few more than default, go figure. Anywho, in order to have icons in gtk2 Deadbeef you HAVE to include a .gtkrc-2.0.mine in your home directory to begin with or they'll get wiped at any ui change. Furthermore, Deadbeef has a setting which allows it to run in gtk3 as well. But then, not only does it fall back on adwaita icons, the icons get resized to a miniscule 16 px as well.
In short, certain gtk2 applications simply REQUIRE a custom gtk2 file and a fully packed iconset ( Qogir dark in the screenshot for crying out loud!) or it will not work.
Screenshot: Deadbeef in gtk2, custom gtk theme and qogir icons. If you don't use a custom gtk2rc file, most icons would be blank ( in the left file manager panel and the right custom toolbar), especially with breeze icons systemwide.
https://imgur.com/a/ApI67Fa