Shader compilation starts every time Material Editor opens with output logs:
LogMaterial: Missing cached shader map for material PreviewMaterial_0, compiling.
LogMaterial: Missing cached shader map for material EmptyMaterial, compiling.
LogMaterial: Missing cached shader map for material EmptyOverheadMaterial, compiling.
LogMaterial: Missing cached shader map for material EmptyMaterial, compiling.
LogMaterial:Warning: FMaterialUniformExpressionTexture had invalid TextureIndex! (1 / 0)
LogMaterial: Missing cached shader map for material EmptyOverheadMaterial, compiling.
LogActorComponent: UnregisterComponent: (/Engine/Transient.SkeletalMeshComponent_0) Not registered. Aborting.
LogActorComponent: UnregisterComponent: (/Engine/Transient.SkeletalMeshComponent_0) Not registered. Aborting.
LogActorComponent: RegisterComponentWithWorld: (/Engine/Transient.MaterialEditorMeshComponent_0) Already registered. Aborting.
LogActorComponent: UnregisterComponent: (/Engine/Transient.SkeletalMeshComponent_0) Not registered. Aborting.
LogActorComponent: RegisterComponentWithWorld: (/Engine/Transient.MaterialEditorMeshComponent_0) Already registered. Aborting.
LogMaterial: Missing cached shader map for material FMatExpressionPreview MaterialExpressionTextureSample_0, compiling.
LogMaterial: Missing cached shader map for material FMatExpressionPreview MaterialExpressionTextureSample_1, compiling.
MaterialEditorStats: Info Base pass shader with only dynamic lighting: 61 instructions
MaterialEditorStats: Info Vertex shader: 33 instructions
MaterialEditorStats: Info Texture samplers: 5/16
UE4.1