So I still have this issue in 424.3… I’ll submit a bug report tonight.
Just changing a TexCoord node from 3, to 4, back to 3, just to make a change, causes ~25k shaders. Just on import to the new version I had over 250K shaders! Ran my machine out of memory 3 times in a row before I could load the level… 
I DO want to say that once I was in, I was getting a 20+ FPS bump over 423, so whatever changes under the rendering hood, they did me right. Looking forward to this getting fixed so I can use up all those empty cycles…