FRPWaitsForNeverException when running with +RTS -N

[noughtmare]

Here's my code:

import Control.FRPNow
import Control.Monad (forever)

ticks :: Now (EvStream ())
ticks = do
  (evs, cbk) <- callbackStream
  async (forever (cbk ()))
  return evs

count :: EvStream () -> Behavior (Behavior Integer)
count = foldEs (\a _ -> a + 1) 0

main :: IO ()
main = runNowMaster $ do
  t <- ticks
  sample $ do
    b <- count t
    when (fmap (> 10000) b)

I have compiled this with -threaded -rtsopts and when running it with +RTS -N it gives me a FRPWaitsForNeverException while it clearly doesn't wait for never. Running it without +RTS -N works just fine.