Varnish 3.0 Guru Meditation with "FetchError TestGunzip error at the very end"

[Glenn Slaven]

I'm getting intermittent guru meditations in varnish (as in I fire 50
requests off and 3 come back bad). In varnishlog it says

   15 VCL_return   c hash
   15 HitPass      c 1394372109
   15 VCL_call     c pass pass
   15 Backend      c 17 default default
   15 TTL          c 1394372164 RFC 0 -1 -1 1384590297 0 1384590291 0 0
   15 VCL_call     c fetch
   15 TTL          c 1394372164 VCL 120 -1 -1 1384590297 -0
   15 VCL_return   c hit_for_pass
   15 ObjProtocol  c HTTP/1.1
   15 ObjResponse  c OK
   15 ObjHeader    c Date: Sat, 16 Nov 2013 08:24:51 GMT
   15 ObjHeader    c Server: Apache
   15 ObjHeader    c Accept-Ranges: bytes
   15 ObjHeader    c Cache-Control: max-age=0, no-cache
   15 ObjHeader    c Vary: Accept-Encoding
   15 ObjHeader    c X-Mod-Pagespeed: 1.5.27.2-2912
   15 ObjHeader    c Content-Encoding: gzip
   15 ObjHeader    c Content-Type: text/html; charset=utf-8
   15 Gzip         c u F - 3755 13624 80 0 0
   15 FetchError   c TestGunzip error at the very end
   15 VCL_call     c error deliver
   15 VCL_call     c deliver deliver
   15 TxProtocol   c HTTP/1.1
   15 TxStatus     c 503
   15 TxResponse   c Service Unavailable

You can see the 15 FetchError c TestGunzip error at the very end which is
the problem. I'm not sure how to interpret the line above Gzip c u F - 3755
13624 80 0 0 and I can't see why this is a problem. The site did not have
any reported problem loading pages before we put varnish in front.

In an assumption that varnish is just being more strict about gzip than the
browsers are, I attempted to turn off the gzip handling, so I set
http_gzip_support to off in /etc/defaults/varnish:

DAEMON_OPTS="-a :80 \
             -T localhost:6082 \
             -f /etc/varnish/default.vcl \
             -S /etc/varnish/secret \
             -s malloc,256m \
             -p http_gzip_support=off"

This has failed to make any difference.  Any help would be greatly
appreciated.
Glenn
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