Forked thread running infinite loop blocks other threads from running

When I compile the following under GHC 7.2.2 with -O1 or -O2, it spins in the forked thread's infinite loop. The forked thread does not yield control to the main thread:

import Control.Concurrent
import Control.Monad

main :: IO ()
main = do
    tid <- forkIO $ forever $ return ()
    putStrLn $ "Forked " ++ show tid

This happens up even if I compile with -threaded -rtsopts, use +RTS -N2, and use forkOS instead of forkIO.

The problem goes away if I disable optimization. It also goes away if I stick a yield :: IO () call in the loop.

Trac metadata

Trac field	Value
Version	7.2.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Runtime System
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