julia> I = Interval(0,1); x = Fun(identity, I); ∂ = Derivative(I);

julia> ∂ * Multiplication(x)
ERROR: AssertionError: spacescompatible(domainspace(ops[k]), rangespace(ops[k + 1]))
Stacktrace:
 [1] TimesOperator{Float64,Tuple{ApproxFun.Infinity{Bool},ApproxFun.Infinity{Bool}}}(::Array{Operator{Float64},1}, ::Tuple{ApproxFun.Infinity{Bool},ApproxFun.Infinity{Bool}}) at /Users/kirill/.julia/packages/ApproxFun/wFAIT/src/Operators/general/algebra.jl:237
 [2] TimesOperator(::Array{Operator{Float64},1}, ::Tuple{ApproxFun.Infinity{Bool},ApproxFun.Infinity{Bool}}) at /Users/kirill/.julia/packages/ApproxFun/wFAIT/src/Operators/general/algebra.jl:271
 [3] TimesOperator(::Array{Operator{Float64},1}) at /Users/kirill/.julia/packages/ApproxFun/wFAIT/src/Operators/general/algebra.jl:274
 [4] promotetimes(::Array{Operator{Float64},1}, ::ApproxFun.UnsetSpace) at /Users/kirill/.julia/packages/ApproxFun/wFAIT/src/Operators/general/algebra.jl:324
 [5] promotetimes(::Array{Operator{Float64},1}) at /Users/kirill/.julia/packages/ApproxFun/wFAIT/src/Operators/general/algebra.jl:328
 [6] *(::ApproxFun.ConcreteDerivative{Chebyshev{Segment{Float64},Float64},Int64,Float64}, ::ApproxFun.ConcreteMultiplication{Chebyshev{Segment{Float64},Float64},ApproxFun.UnsetSpace,Float64}) at /Users/kirill/.julia/packages/ApproxFun/wFAIT/src/Operators/general/algebra.jl:535
 [7] top-level scope at none:0

# But this works:
julia> ∂[x]
TimesOperator:Chebyshev(【0.0,1.0】)→Ultraspherical(1,【0.0,1.0】)
 1.0  1.0  0.5   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   ⋅
  ⋅   1.0  2.0  1.0   ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   ⋅
  ⋅    ⋅   1.5  3.0  1.5   ⋅    ⋅    ⋅    ⋅    ⋅   ⋅
  ⋅    ⋅    ⋅   2.0  4.0  2.0   ⋅    ⋅    ⋅    ⋅   ⋅
  ⋅    ⋅    ⋅    ⋅   2.5  5.0  2.5   ⋅    ⋅    ⋅   ⋅
  ⋅    ⋅    ⋅    ⋅    ⋅   3.0  6.0  3.0   ⋅    ⋅   ⋅
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   3.5  7.0  3.5   ⋅   ⋅
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   4.0  8.0  4.0  ⋅
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   4.5  9.0  ⋱
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   5.0  ⋱
  ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅    ⋅   ⋱

julia> versioninfo()
Julia Version 1.0.1
Commit 0d713926f8 (2018-09-29 19:05 UTC)
Platform Info:
  OS: macOS (x86_64-apple-darwin14.5.0)
  CPU: Intel(R) Core(TM) i7-4770HQ CPU @ 2.20GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-6.0.0 (ORCJIT, haswell)

julia> Pkg.status()
    Status `~/.julia/environments/v1.0/Project.toml`
  [28f2ccd6] ApproxFun v0.9.0
... etc