pasting pattern causes Unmarshal error with hiddenRoutes

[nikhan]

pasting this

{"blocks":[{"label":"","type":"delay","id":1,"inputs":[{"name":"in","value":{"data":"foo"},"type":"any"},{"name":"duration","value":{"data":"5s"},"type":"string"}],"outputs":[{"name":"out","type":"any"}],"source":null,"position":{"x":-158,"y":-4}},{"label":"","type":"identity","id":2,"inputs":[{"name":"in","value":null,"type":"any"}],"outputs":[{"name":"out","type":"any"}],"source":null,"position":{"x":-1,"y":-5}},{"label":"","type":"log","id":3,"inputs":[{"name":"log","value":null,"type":"any"}],"outputs":[],"source":null,"position":{"x":158,"y":6}}],"sources":[],"links":[],"connections":[{"from":{"id":1,"route":0},"to":{"id":2,"route":0},"id":4},{"from":{"id":2,"route":0},"to":{"id":3,"route":0},"id":5}],"groups":[{"id":6,"label":"","children":[1,2,3],"position":{"x":-33,"y":-41},"hiddenRoutes":["1_1_input","1_0_input","1_0_output","2_0_input","2_0_output","3_0_input"]}]}

leads to this:

2015/11/25 10:10:21 http: panic serving [::1]:58187: interface conversion: string is not error: missing method Error
goroutine 6 [running]:
net/http.func·011()
    /usr/local/go/src/net/http/server.go:1130 +0xbb
encoding/json.func·001()
    /usr/local/go/src/encoding/json/decode.go:137 +0xa7
github.com/nytlabs/st-core/server.HiddenRoutesLedger.UnmarshalJSON(0x0, 0xc20825c328, 0x4b, 0x2d8, 0x0, 0x0)
    /Users/204272/go/src/github.com/nytlabs/st-core/server/group.go:57 +0x18d
github.com/nytlabs/st-core/server.(*HiddenRoutesLedger).UnmarshalJSON(0xc2080de408, 0xc20825c328, 0x4b, 0x2d8, 0x0, 0x0)
    <autogenerated>:2 +0xc5