wrong derivative with array concatenation

My code used to work in ReverseDiff 1.2.0 but the current version (1.4.2) returns the wrong derivatives. I've stripped away everything to a MWE:

import ForwardDiff
import ReverseDiff

struct Test{TF}
    a::TF
end

function func(x)
    tvec = Test.(x[1:2])
    a = [t.a for t in tvec]
    return sum([a; x[3]])
end

x = [1.0, 2.0, 3.0]
J1 = ForwardDiff.gradient(func, x)
J2 = ReverseDiff.gradient(func, x)

The answer should be [1, 1, 1], but ReverseDiff gives [0, 0, 1]. If I revert back to 1.2 then it works as expected. Trying different versions it seems that from 1.3 onward this no longer works.

Reproduce the minimal example using ForwardDiff.gradient and ReverseDiff.gradient on func, comparing ReverseDiff 1.2.0 with 1.3 and 1.4.2. Investigate the derivative path for the array concatenation in return sum([a; x[3]]); done means ReverseDiff.gradient returns [1, 1, 1] in the current version.