New vcat not working

a = 1
s = zpk("s")
base = ss((a-s)/(a+s))
Qq = [ss(1.);base;[balreal(base^k)[1] for k = 2:10-1]] # Does not work
Qq = [ss(1.);base;[balreal(base^k)[1] for k = 2:10-1]...] # Works

Still a problem 2019-01-30
Still a problem 2020-10-10

ERROR: MethodError: Cannot `convert` an object of type Array{StateSpace{Float64,Array{Float64,2}},1} to an object of type StateSpace{Float64,Array{Float64,2}}
Closest candidates are:
  convert(::Type{StateSpace{T,MT}}, ::AbstractArray{#s28,2} where #s28<:Number) where {T, MT} at /local/home/fredrikb/.julia/dev/ControlSystems/src/types/conversion.jl:25
  convert(::Type{StateSpace{T,MT}}, ::Number) where {T, MT} at /local/home/fredrikb/.julia/dev/ControlSystems/src/types/conversion.jl:36
  convert(::Type{StateSpace{T,MT}}, ::StateSpace) where {T, MT} at /local/home/fredrikb/.julia/dev/ControlSystems/src/types/conversion.jl:58
  ...
Stacktrace:
 [1] _broadcast_getindex_evalf at ./broadcast.jl:582 [inlined]
 [2] _broadcast_getindex at ./broadcast.jl:565 [inlined]
 [3] (::getfield(Base.Broadcast, Symbol("##17#18")){Base.Broadcast.Broadcasted{Base.Broadcast.Style{Tuple},Nothing,typeof(convert),Tuple{Base.RefValue{Type{StateSpace{Float64,Array{Float64,2}}}},Tuple{StateSpace{Float64,Array{Float64,2}},StateSpace{Float64,Array{Float64,2}},Array{StateSpace{Float64,Array{Float64,2}},1}}}}})(::Int64) at ./broadcast.jl:954
 [4] ntuple at ./tuple.jl:158 [inlined]
 [5] tuplebroadcast at ./broadcast.jl:954 [inlined]
 [6] copy at ./broadcast.jl:952 [inlined]
 [7] materialize at ./broadcast.jl:756 [inlined]
 [8] _cat_t at /local/home/fredrikb/.julia/dev/ControlSystems/src/connections.jl:115 [inlined]
 [9] #cat_t#99 at ./abstractarray.jl:1353 [inlined]
 [10] #cat_t at ./none:0 [inlined]
 [11] _cat at ./abstractarray.jl:1351 [inlined]
 [12] #cat#100 at ./abstractarray.jl:1480 [inlined]
 [13] #cat at ./none:0 [inlined]
 [14] vcat(::StateSpace{Float64,Array{Float64,2}}, ::StateSpace{Float64,Array{Float64,2}}, ::Array{StateSpace{Float64,Array{Float64,2}},1}) at ./abstractarray.jl:1418
 [15] top-level scope at none:0

Start with the vcat reproduction in the issue and inspect src/connections.jl around line 115, where the stack trace enters _cat_t. Compare the failing array argument with the working splatted form, then add a regression test showing both forms behave consistently. Done means the unsplatted vcat example no longer raises the reported conversion error.