Sub-project cannot be "resolved"

I'm playing around with Play's sub-project functionality, but my sub-project seems to be treated as a library dependency and, of course, cannot be resolved.

I started with the play-scala template from Activator, and then followed the first section of these docs pretty much exactly: https://www.playframework.com/documentation/2.3.x/SBTSubProjects. I pushed the result here: https://github.com/khy/multi-test.

I'm using Activator 1.2.10, Play 2.3.4, sbt 0.13.5 and Scala 2.11.1. The result of running `sbt compile` is *always* the following:
```bash
[multi-test] $ compile
[info] Updating {file:/Users/khy/Code/multi-test/}myLibrary...
[info] Resolving org.fusesource.jansi#jansi;1.4 ...
[info] Done updating.
[info] Updating {file:/Users/khy/Code/multi-test/}root...
[info] Resolving org.scala-lang#scala-library;2.11.1 ...
[info] Compiling 1 Scala source to /Users/khy/Code/multi-test/myLibrary/target/scala-2.10/classes...
[info] Resolving mylibrary#mylibrary_2.11;0.1-SNAPSHOT ...
[warn] 	module not found: mylibrary#mylibrary_2.11;0.1-SNAPSHOT
[warn] ==== local: tried
[warn]   /Users/khy/.ivy2/local/mylibrary/mylibrary_2.11/0.1-SNAPSHOT/ivys/ivy.xml
[warn] ==== public: tried
[warn]   http://repo1.maven.org/maven2/mylibrary/mylibrary_2.11/0.1-SNAPSHOT/mylibrary_2.11-0.1-SNAPSHOT.pom
[warn] ==== Typesafe Releases Repository: tried
[warn]   http://repo.typesafe.com/typesafe/releases/mylibrary/mylibrary_2.11/0.1-SNAPSHOT/mylibrary_2.11-0.1-SNAPSHOT.pom
[info] Resolving jline#jline;2.11 ...
[warn] 	::::::::::::::::::::::::::::::::::::::::::::::
[warn] 	::          UNRESOLVED DEPENDENCIES         ::
[warn] 	::::::::::::::::::::::::::::::::::::::::::::::
[warn] 	:: mylibrary#mylibrary_2.11;0.1-SNAPSHOT: not found
[warn] 	::::::::::::::::::::::::::::::::::::::::::::::
[trace] Stack trace suppressed: run last root/*:update for the full output.
[error] (root/*:update) sbt.ResolveException: unresolved dependency: mylibrary#mylibrary_2.11;0.1-SNAPSHOT: not found
[error] Total time: 7 s, completed Sep 2, 2014 10:02:10 PM
```

Any idea what is going wrong?