Migrated from http://lampsvn.epfl.ch/trac/scala/ticket/2689
Reporter spiros
This happen when the code has compilation errors and the bogus error messages persist even if we fix the code and recompile.
How to trigger the bug # Create a file A.scala and save it to compile

//file: /bugs/A.scala
package bugs
class A

# Create a file B.scala with two classes B and C and save it to compile

//file: /bugs/B.scala
package bugs
class B(a: A, c: C)
class C

# Comment out class C in B.scala and save the file (no error appears because of #2581)

1. Do a Clean and Build

At this stage the Problems View has one error (that appears twice) not found type: C, but the editor has two errors (they also appear twice) one for class C and one for class A (_not found type: A_). The problem here is that class A is valid and compiled (the A.class file exists on disk and the compilation was a result of a clean operation in Eclipse).
Now if we uncomment the class C in file B.scala (to bring the code in a correct state again) and save the file to trigger a compilation, all the files get compiled, the error gets removed from the Problems View but the bogus error for class A still exists in the editor. To remove this bogus message we need to do again a Clean&Build.
I found this bug while investigating the bug outlined in  this message and I suspect that they might be related.
Tested with Eclipse 3.5.1 and SDT r19784.

class A
class B

class C {
  val a: A = new B
}