<socket: 1796>: hPutBuf: illegal operation (handle is finalized)

I´m a bit lost trying to find the source of this error.  

I´m running an hack application  (package hack). Basically it is a handler of web requests. 

hack can be used with different web servers: Hyena, simpleserver, HappStack....

all of them produce this error after a few interactions.,  Supposedly, it happens within the socket module

since neither my module, nor hack, nor the hack simpleserver (package hack-handler-simpleserver) call explicitly hPutBuf

I tried to reproduce the error under linux, but my ubuntu installation is too old and I´m in the process of reinstalling everything again.

In the meantime, Any of you can give me any hint about the error?