Zygote cannot repeat?

[nmheim]

using Flux

struct Model
    W
end

Flux.@functor Model

m = Model(rand(3))
ps = params(m)

loss() = sum(repeat(m.W, 1, 4))
# loss() = sum(m.W)
gs = Flux.gradient(loss, ps)

the example above works with the loss that is commented out.
with the one that contains a repeat I get:

ERROR: LoadError: Mutating arrays is not supported
Stacktrace:
 [1] error(::String) at ./error.jl:33
 [2] (::Zygote.var"#982#983")(::Nothing) at /home/niklas/.julia/packages/Zygote/8dVxG/src/lib/array.jl:38
 [3] (::Zygote.var"#2597#back#984"{Zygote.var"#982#983"})(::Nothing) at /home/niklas/.julia/packages/ZygoteRules/6nssF/src/adjoint.jl:49
 [4] repeat at ./abstractarraymath.jl:283 [inlined]
 [5] (::typeof(∂(repeat)))(::FillArrays.Fill{Float64,2,Tuple{Base.OneTo{Int64},Base.OneTo{Int64}}}) at /home/niklas/.julia/packages/Zygote/8dVxG/src/compiler/interface2.jl:0
 [6] loss at /home/niklas/repos/GenerativeModels.jl/minimal.jl:12 [inlined]
 [7] (::typeof(∂(loss)))(::Float64) at /home/niklas/.julia/packages/Zygote/8dVxG/src/compiler/interface2.jl:0
 [8] (::Zygote.var"#38#39"{Zygote.Params,Zygote.Context,typeof(∂(loss))})(::Float64) at /home/niklas/.julia/packages/Zygote/8dVxG/src/compiler/interface.jl:101
 [9] gradient(::Function, ::Zygote.Params) at /home/niklas/.julia/packages/Zygote/8dVxG/src/compiler/interface.jl:47
 [10] top-level scope at /home/niklas/repos/GenerativeModels.jl/minimal.jl:13
 [11] include at ./boot.jl:328 [inlined]
 [12] include_relative(::Module, ::String) at ./loading.jl:1105
 [13] include(::Module, ::String) at ./Base.jl:31
 [14] include(::String) at ./client.jl:424
 [15] top-level scope at REPL[5]:1

[nmheim]

Works by using inner keyword in repeat or by broacasting with .*ones(...)