Asynchronous concurrency gets Reduce confused

The following test works. But take out the Semaphore and it hangs and/or scrambles the results. Perhaps Reduce.jl should be using a semaphore/mutex internally? This problem arose when I was using Reduce.jl with Genie.jl, and it caused some hard to debug problems, such as one HTTP request hanging until the next request came in, or having rcall return the result from someone else's query.

using Reduce

reduce_sem = Base.Semaphore(1)

println("create")
tasks = []
for i in 1:10
t = @task begin
println("begin $i")
Base.acquire(reduce_sem)
println("rcall $i")
y = :($i * x) |> rcall
println("$i -> $y")
Base.release(reduce_sem)
println("released")
end
push!(tasks, t)
end

println("schedule")
for t in tasks
schedule(t)
end

println("wait")
for t in tasks
wait(t)
end