So there are these strange flickers in the sky only on Iris 1.8.0, was not present on 1.7.0 which is quite strange. I have attached a video. All other shaders work perfectly fine.

Had the same issue, resolved by disabling 3d Skin Layers as mentioned above - along with Better Animations as well.

As a side note, tried reverting the change of DH_solid.vsh on gl_Position = dhProjection * gl_ModelViewMatrix * gl_Vertex; line as posted elsewhere, but didn't seem to effect anything (though that was a fairly old post hehe). Latest dev build is running like a dream, thank you!

most likely caused by 3d skin layers mod if you have it.