While playing with the latest 2.8 snapshot (r18215-b20090706020217 to be precise) I noticed that a package object containing a case class gets an assertion failure when re-compiling (i.e., the class files already exist from a previous run, even a previous build of the exact same source). A minimal test case:

package object foo {
case class X()
}

And the error:

Exception in thread "main" java.lang.AssertionError: assertion failed: List(object package$$X, object package$$X)
at scala.Predef$$.assert(Predef.scala:97)
at scala.tools.nsc.symtab.Symbols$$Symbol.suchThat(Symbols.scala:988)
at scala.tools.nsc.symtab.Symbols$$Symbol.linkedModuleOfClass(Symbols.scala:1159)
at scala.tools.nsc.backend.jvm.GenJVM$$BytecodeGenerator.genClass(GenJVM.scala:203)
at scala.tools.nsc.backend.jvm.GenJVM$$JvmPhase$$$$anonfun$$run$$2.apply(GenJVM.scala:50)
at scala.tools.nsc.backend.jvm.GenJVM$$JvmPhase$$$$anonfun$$run$$2.apply(GenJVM.scala:50)
at scala.collection.Iterator$$class.foreach(Iterator.scala:500)
at scala.collection.generic.MapTemplate$$$$anon$$4.foreach(MapTemplate.scala:156)
at scala.tools.nsc.backend.jvm.GenJVM$$JvmPhase.run(GenJVM.scala:50)
at scala.tools.nsc.Global$$Run.compileSources(Global.scala:781)
at scala.tools.nsc.Global$$Run.compile(Global.scala:855)
at scala.tools.nsc.Main$$.process(Main.scala:75)
at scala.tools.nsc.Main$$.main(Main.scala:89)
at scala.tools.nsc.Main.main(Main.scala)

A normal class does not cause the failure; nor does a case object.