Mapping observable leads to world age error

[yha]

After running:

obs = Observable(0)
t = @task for n=1:10
    obs[] = n
    sleep(1)
end

schedule(t)
sleep(1)
map(x->2x, obs)
# This alternative works:
# f(x) = 2x
# map(f, obs)

julia> obs
Observable{Int64} with 1 listeners. Value:
2

julia> t
Task (failed) @0x0000000017b7e290
MethodError: no method matching (::var"#127#128")(::Int64)
The applicable method may be too new: running in world age 27995, while current world is 27996.
Closest candidates are:
  #127(::Any) at untitled-975cdec0428a7c38d7a195fd90bb4d35:16 (method too new to be called from this world context.)
[...]

(on 0.3.2, julia 1.5.2)

EDIT: looks like it's irrelevant the the function is anonymous. The issue also occurs with a named function, provided it's a new function (no applicable method existed when the task was compiled).