projector crash with "fatal error: concurrent map read and map write"

4.5.0-2550 system test run with forestdb projector crashed during a rebalance
fatal error: concurrent map read and map write

goroutine 26544 [running]:
runtime.throw(0xeb8480, 0x21)
/home/couchbase/.cbdepscache/exploded/x86_64/go-1.6/go/src/runtime/panic.go:530 +0x90 fp=0xc861ee9838 sp=0xc861ee9820
runtime.mapaccess1_faststr(0xaec080, 0xc820232180, 0xc8608b23c5, 0x1f, 0x2)
/home/couchbase/.cbdepscache/exploded/x86_64/go-1.6/go/src/runtime/hashmap_fast.go:202 +0x5b fp=0xc861ee9898 sp=0xc861ee9838
github.com/couchbase/indexing/secondary/adminport.(*httpServer).systemHandler(0xc8201700c0, 0x7f1451916668, 0xc87001e5b0, 0xc86f12afc0)
/home/couchbase/jenkins/workspace/watson-unix/goproj/src/github.com/couchbase/indexing/secondary/adminport/admin_httpd.go:236 +0x260 fp=0xc861ee9ad0 sp=0xc861ee9898
github.com/couchbase/indexing/secondary/adminport.(*httpServer).(github.com/couchbase/indexing/secondary/adminport.systemHandler)-fm(0x7f1451916668, 0xc87001e5b0, 0xc86f12afc0)
/home/couchbase/jenkins/workspace/watson-unix/goproj/src/github.com/couchbase/indexing/secondary/adminport/admin_httpd.go:89 +0x3e fp=0xc861ee9af8 sp=0xc861ee9ad0
net/http.HandlerFunc.ServeHTTP(0xc82015f360, 0x7f1451916668, 0xc87001e5b0, 0xc86f12afc0)
/home/couchbase/.cbdepscache/exploded/x86_64/go-1.6/go/src/net/http/server.go:1618 +0x3a fp=0xc861ee9b18 sp=0xc861ee9af8
net/http.(*ServeMux).ServeHTTP(0xc8202321e0, 0x7f1451916668, 0xc87001e5b0, 0xc86f12afc0)
/home/couchbase/.cbdepscache/exploded/x86_64/go-1.6/go/src/net/http/server.go:1910 +0x17d fp=0xc861ee9b70 sp=0xc861ee9b18
net/http.serverHandler.ServeHTTP(0xc820174000, 0x7f1451916668, 0xc87001e5b0, 0xc86f12afc0)
/home/couchbase/.cbdepscache/exploded/x86_64/go-1.6/go/src/net/http/server.go:2081 +0x19e fp=0xc861ee9bd0 sp=0xc861ee9b70
net/http.(*conn).serve(0xc82f77fd80)
/home/couchbase/.cbdepscache/exploded/x86_64/go-1.6/go/src/net/http/server.go:1472 +0xf2e fp=0xc861ee9f98 sp=0xc861ee9bd0
runtime.goexit()
/home/couchbase/.cbdepscache/exploded/x86_64/go-1.6/go/src/runtime/asm_amd64.s:1998 +0x1 fp=0xc861ee9fa0 sp=0xc861ee9f98
created by net/http.(*Server).Serve
/home/couchbase/.cbdepscache/exploded/x86_64/go-1.6/go/src/net/http/server.go:2137 +0x44e

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