Working on the Go package, I found that the grafting procedure fails in
a way that I don't understand:

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$ ./pre-inst-env guix build go@1.9
The following derivation will be built:
   /gnu/store/bv30jxzjl7c5z3hk6pmywpzwwrn1hq5m-go-1.9rc1.drv
@ build-started /gnu/store/bv30jxzjl7c5z3hk6pmywpzwwrn1hq5m-go-1.9rc1.drv - x86_64-linux /var/log/guix/drvs/bv//30jxzjl7c5z3hk6pmywpzwwrn1hq5m-go-1.9rc1.drv.bz2
grafting '/gnu/store/8zbi5rr5q2pxksfgpxq37m60nsa21d3v-go-1.9rc1-doc' -> '/gnu/store/6v24sf0b3hgyc80b4w2yvx1aw03zinw6-go-1.9rc1-doc'...
grafting '/gnu/store/73fvsx0qizcrbajgjwn8mkzkpxa6abx4-go-1.9rc1' -> '/gnu/store/ghg75mjw3csiv9hf7q0cxrm1g0fx5d0k-go-1.9rc1'...
ERROR: In procedure put-bytevector: Value out of range: 0
builder for `/gnu/store/bv30jxzjl7c5z3hk6pmywpzwwrn1hq5m-go-1.9rc1.drv' failed with exit code 1
@ build-failed /gnu/store/bv30jxzjl7c5z3hk6pmywpzwwrn1hq5m-go-1.9rc1.drv - 1 builder for `/gnu/store/bv30jxzjl7c5z3hk6pmywpzwwrn1hq5m-go-1.9rc1.drv' failed with exit code 1
guix build: error: build failed: build of `/gnu/store/bv30jxzjl7c5z3hk6pmywpzwwrn1hq5m-go-1.9rc1.drv' failed
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This doesn't happen with the previous release, go1.9beta2. For both
releases, the ungrafted Go seems to work.

I'll keep digging...