matthieu,

i may be experiencing the same issue. built a filter which sends a subrequest to a location different from the parent request. in my scenario i've seen both the parent and subrequest called first (varnishlog), haven't been able to figure out why the order in which requests are called is not consistent. from the nginx error log it appears that parent request is written to a temporary file and when the subrequest is returned from upstream my page will hang. there must be a way to finalize the request and force the buffer to written to the client.

peter