I can confirm that with the new package gtk2-engines-oxygen_1.3.3-2ubuntu0.1_amd64.deb EasyTag is starting correctly (I'm not using Emacs but EasyTag had the exact same problem)
I can confirm that with the new package gtk2-engines- oxygen_ 1.3.3-2ubuntu0. 1_amd64. deb EasyTag is starting correctly (I'm not using Emacs but EasyTag had the exact same problem)