Keyword arguments parametric types break matching

[lostella]

This works on Julia 1.0.3

julia> f(a::C) where {R <: Real, C <: Union{R, Complex{R}}} = println(R)
f (generic function with 1 method)

julia> f(Float64(3))
Float64

julia> f(Float32(3)+Float32(2)im)
Float32

but the following does not

julia> g(a::C; b=R(1)) where {R <: Real, C <: Union{R, Complex{R}}} = println(R)
ERROR: UndefVarError: R not defined
Stacktrace:
 [1] top-level scope at none:0

Discussion here: https://discourse.julialang.org/t/type-matching-with-positional-vs-keyword-arguments/19854