It appears that the commit for #13218 changed the behavior of the GetHostConfig() wrapper in runconfig/config.go and broke the remote API for container/create

The change was part of this:

diff --git a/runconfig/config.go b/runconfig/config.go
index 74e8bd6..8c578ee 100644
--- a/runconfig/config.go
+++ b/runconfig/config.go
[snip]

-func (c ContainerConfigWrapper) HostConfig() *HostConfig {
-       if c.hostConfigWrapper == nil {
-               return new(HostConfig)
+func (w *ContainerConfigWrapper) GetHostConfig() *HostConfig {
+       hc := w.HostConfig

[snip]

This function used to return a new(HostConfig) when nil was passed.

This change ended up breaking the remote API. If a client does not specify the HostConfig object in the API request for /container/create, the server linux code ends up dereferencing the HostConfig pointer it thought was non-nil.

api/server/server.go

      config, hostConfig, err := runconfig.DecodeContainerConfig(r.Body)
      if err != nil {
          return err
      }
      adjustCpuShares(version, hostConfig)

api/server/server_linux.go
  func adjustCpuShares(version version.Version, hostConfig *runconfig.HostConfig) {
      if version.LessThan("1.19") {                                          
          if hostConfig.CpuShares > 0 {

This causes the following backtrace:

2015/07/23 15:09:29 http: panic serving @: runtime error: invalid memory address or nil pointer dereference
goroutine 158 [running]:
net/http.func·011()
/usr/local/go/src/net/http/server.go:1130 +0xbb
github.com/docker/docker/api/server.adjustCpuShares(0xc20abea097, 0x4, 0x0)
/go/src/github.com/docker/docker/api/server/server_linux.go:112 +0x61
github.com/docker/docker/api/server.(_Server).postContainersCreate(0xc2080bb580, 0xc20abea097, 0x4, 0x7f276d88e7d8, 0xc2089f5680, 0xc2085f4ea0, 0xc20abea270, 0x0, 0x0)
/go/src/github.com/docker/docker/api/server/server.go:926 +0x21a
github.com/docker/docker/api/server._Server.(github.com/docker/docker/api/server.postContainersCreate)·fm(0xc20abea097, 0x4, 0x7f276d88e7d8, 0xc2089f5680, 0xc2085f4ea0, 0xc20abea270, 0x0, 0x0)
/go/src/github.com/docker/docker/api/server/server.go:1569 +0x7b
github.com/docker/docker/api/server.func·008(0x7f276d88e7d8, 0xc2089f5680, 0xc2085f4ea0)
/go/src/github.com/docker/docker/api/server/server.go:1525 +0xc8f
net/http.HandlerFunc.ServeHTTP(0xc20818af80, 0x7f276d88e7d8, 0xc2089f5680, 0xc2085f4ea0)
/usr/local/go/src/net/http/server.go:1265 +0x41
github.com/gorilla/mux.(_Router).ServeHTTP(0xc2080a3ae0, 0x7f276d88e7d8, 0xc2089f5680, 0xc2085f4ea0)
/go/src/github.com/docker/docker/vendor/src/github.com/gorilla/mux/mux.go:98 +0x297
net/http.serverHandler.ServeHTTP(0xc2081ba120, 0x7f276d88e7d8, 0xc2089f5680, 0xc2085f4ea0)
/usr/local/go/src/net/http/server.go:1703 +0x19a
net/http.(_conn).serve(0xc208a720a0)
/usr/local/go/src/net/http/server.go:1204 +0xb57
created by net/http.(*Server).Serve
/usr/local/go/src/net/http/server.go:1751 +0x35e

$ bundles/latest/dynbinary/docker version
Client:
Version: 1.8.0-dev
API version: 1.20
Go version: go1.4.2
Git commit: 899c3e9-dirty
Built: Thu Jul 23 19:22:21 UTC 2015
OS/Arch: linux/amd64
Experimental: true

Reproduces every time if a remote API client specifies a /container/create with no HostConfig object specified in the request.