Why is this type inference failed

General Usage
1 
function interfer_test(
    obj::T,
    Ls::NTuple{2,<:Integer},
) where {T}
    CT = complex(T)
    mem_init = ntuple(_ -> zeros(CT, Ls), Val(4))
end
@code_warntype interfer_test(1,(100,100))

The above code returns

Variables
  #self#::Core.Const(interfer_test)
  obj::Int64
  Ls::Tuple{Int64, Int64}
  #33::var"#33#34"{Tuple{Int64, Int64}, DataType}
  mem_init::NTuple{4, Matrix{_A} where _A}
  CT::Type{Complex{Int64}}

Body::NTuple{4, Matrix{_A} where _A}
1 ─      (CT = Main.complex($(Expr(:static_parameter, 1))))
│   %2 = Main.:(var"#33#34")::Core.Const(var"#33#34")
│   %3 = Core.typeof(Ls)::Core.Const(Tuple{Int64, Int64})
│   %4 = Core.typeof(CT::Core.Const(Complex{Int64}))::Core.Const(DataType)
│   %5 = Core.apply_type(%2, %3, %4)::Core.Const(var"#33#34"{Tuple{Int64, Int64}, DataType})
│        (#33 = %new(%5, Ls, CT::Core.Const(Complex{Int64})))
│   %7 = #33::var"#33#34"{Tuple{Int64, Int64}, DataType}
│   %8 = Main.Val(4)::Core.Const(Val{4}())
│   %9 = Main.ntuple(%7, %8)::NTuple{4, Matrix{_A} where _A}
│        (mem_init = %9)
└──      return %9

It seems the inferred CT wasn’t transmitted into the anonymous function.
I tried this code on 1.5.1 ,1.6.1 and Master, and the results are similar.

2

By the way, the following is ok

function interfer_test(obj::T, Ls::NTuple{2,<:Integer}) where {T}
    CT = complex(T)
    mem_init = ntuple(_ -> zeros(CT, (100,100)), Val(4))
end
@code_warntype interfer_test(1,(100,100))

which returns

Variables
  #self#::Core.Const(interfer_test)
  obj::Int64
  Ls::Tuple{Int64, Int64}
  #35::var"#35#36"{DataType}
  mem_init::NTuple{4, Matrix{Complex{Int64}}}
  CT::Type{Complex{Int64}}

Body::NTuple{4, Matrix{Complex{Int64}}}
1 ─      (CT = Main.complex($(Expr(:static_parameter, 1))))
│   %2 = Main.:(var"#35#36")::Core.Const(var"#35#36")
│   %3 = Core.typeof(CT::Core.Const(Complex{Int64}))::Core.Const(DataType)
│   %4 = Core.apply_type(%2, %3)::Core.Const(var"#35#36"{DataType})
│        (#35 = %new(%4, CT::Core.Const(Complex{Int64})))
│   %6 = #35::Core.Const(var"#35#36"{DataType}(Complex{Int64}))::Core.Const(var"#35#36"{DataType}(Complex{Int64}))
│   %7 = Main.Val(4)::Core.Const(Val{4}())
│   %8 = Main.ntuple(%6, %7)::NTuple{4, Matrix{Complex{Int64}}}
│        (mem_init = %8)
└──      return %8