sbt assembly can't find type in the same package

Question

I have the code shown here http://scastie.org/10156

report the error

when running sbt 0.13.8
plugin assembly
I get
[error] /home/xx/workspace/sync-hsae-middleware/src/test/scala/com/example/MyServiceSpec.scala:8: not found: type MyService
[error] class MyServiceSpec extends Specification with Specs2RouteTest with MyService {
[error]                                                                     ^
[error] /home/xx/workspace/sync-hsae-middleware/src/test/scala/com/example/MyServiceSpec.scala:14: not found: value myRoute
[error]       Get() ~> myRoute ~> check {
[error]                ^
[error] two errors found
[error] (test:compileIncremental) Compilation failed
[error] Total time: 5 s, completed 10/06/2015 15:00:15

*/

I can't figure out what is the issue because when I use sbt run it works well.