The following program:

module Main where

import Control.Concurrent

main :: IO ()
main = do
    todo <- newChan
    forkIO $ readChan todo
    putStrLn "Before isEmptyChan"
    b <- isEmptyChan todo
    putStrLn "After isEmptyChan"
    writeChan todo ()

Gives the output:

$ ghc --make Main.hs -threaded && ./Main.exe
Before isEmptyChan
Main.exe: thread blocked indefinitely in an MVar operation

I think that's a bug. Note that if the putStrLn statements are removed then it works, but I think that's because the printing introduces a delay that lets the other thread run.