Ah, true. The problem is that the @unpack macro expands to ~12 lines of code, so breakpoints on the next few lines actually stop you in @unpack.
The best solution right now is probably to use JuliaInterpreters @bp macro like
function testA(varA::A)
@unpack a = varA
@bp
println(a)
end
Juno.@run testA(A())