The code

   interface X extends W{}
   class W implements X{}

makes a stack overflow in 1.1.5, and

sun.tools.java.CompilerError: checkMeet(), no abstract method
        at sun.tools.java.MemberDefinition.checkMeet(MemberDefinition.java:590)
        at sun.tools.java.ClassDefinition.collectOneClass(ClassDefinition.java:1209)
        at sun.tools.java.ClassDefinition.collectInheritedMethods(ClassDefinition.java:1337)
        at sun.tools.java.ClassDefinition.getInheritableMethods(ClassDefinition.java:1359)
        at sun.tools.java.ClassDefinition.collectOneClass(ClassDefinition.java:1092)
        at sun.tools.java.ClassDefinition.collectInheritedMethods(ClassDefinition.java:1337)
        at sun.tools.javac.SourceClass.basicCheck(SourceClass.java:1103)
        at sun.tools.java.ClassDeclaration.getClassDefinition(ClassDeclaration.java:122)
        at sun.tools.javac.SourceClass.checkSupers(SourceClass.java:774)
        at sun.tools.javac.SourceClass.resolveTypeStructure(SourceClass.java:1197)
        at sun.tools.javac.SourceClass.basicCheck(SourceClass.java:1050)
        at sun.tools.java.ClassDeclaration.getClassDefinition(ClassDeclaration.java:122)
        at sun.tools.javac.Main.compile(Main.java:345)
        at sun.tools.javac.Main.main(Main.java:571)

in 1.2beta3.