hClose non-terminating

I have a problem with a handle for which hClose does not terminate.  
Unfortunately
it's too much work for me to narrow it down now, but perhaps it can be worked 
out
from these facts?
(1) it's a socket connection.
(2) it has BlockBuffering (Just 4096) set.
(3) it is possible that another thread is simultaneously trying to read from it.
(4) hFlush on the same handle terminates.
(5) if I remove the hClose the program terminates (presumably closing the 
connection)
successfully.