Version 1.5.12, getting 502 when server check fails, but server is still working

[Shawn Heisey]

I'm working on making my application capable of handling service 
restarts on the back end with zero loss or interruption.  It runs on two 
servers behind haproxy.

At application shutdown, I'm setting a flag that makes the healthcheck 
fail, and then keeping the application running for thirty seconds in 
order to finish up all requests that the server has already received.

It seems that when haproxy's health check fails while a request is 
underway, the machine making the request will be sent a 502 response 
instead of the good response that the server WILL make. This is probably 
a good thing for haproxy to do in general, but in this case, I know that 
my application's shutdown hook *WILL* allow enough time for the request 
to finish before it forcibly halts the application.

Is there a config option I can enable to allow in-flight responses to be 
returned after check failure?  Would I need to upgrade beyond 1.5 to get 
that working?  If the server doesn't send a good response within the 
timeout limit, then I'm perfectly OK with haproxy returning an error.

Thanks,
Shawn