FULL PRODUCT VERSION :
java version "1.6.0_37"
Java(TM) SE Runtime Environment (build 1.6.0_37-b06)
Java HotSpot(TM) 64-Bit Server VM (build 20.12-b01, mixed mode)

java version "1.7.0_45"
Java(TM) SE Runtime Environment (build 1.7.0_45-b18)
Java HotSpot(TM) 64-Bit Server VM (build 24.45-b08, mixed mode)

java version "1.8.0-ea"
Java(TM) SE Runtime Environment (build 1.8.0-ea-b109)
Java HotSpot(TM) 64-Bit Server VM (build 25.0-b51, mixed mode)

A DESCRIPTION OF THE PROBLEM :
This code used to compile in JDK 1.6.0_37, but does not compiles in JDK 1.7.0_45 nor in JDK 1.8.0-ea-b109:

interface A {}

abstract class B<X> {
    abstract X m();
}

abstract class C<Y> extends B<Y> {
    @Override
    abstract Y m();
}

class MyBug<Z extends C<?> & A> {}


REGRESSION. Last worked in version 6u43

ADDITIONAL REGRESSION INFORMATION:
java version "1.6.0_37"
Java(TM) SE Runtime Environment (build 1.6.0_37-b06)
Java HotSpot(TM) 64-Bit Server VM (build 20.12-b01, mixed mode)

java version "1.7.0_45"
Java(TM) SE Runtime Environment (build 1.7.0_45-b18)
Java HotSpot(TM) 64-Bit Server VM (build 24.45-b08, mixed mode)

java version "1.8.0-ea"
Java(TM) SE Runtime Environment (build 1.8.0-ea-b109)
Java HotSpot(TM) 64-Bit Server VM (build 25.0-b51, mixed mode)

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the program using JDK 1.7.0 or JDK 8 EA b109.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The code should compile in JDK 7 and JDK 8, as it used to compile in JDK 6.
ACTUAL -
error: m() in C cannot override m() in B
class MyBug<Z extends C<?> & A> {}
  return type CAP#1 is not compatible with CAP#2
  where Y,X are type-variables:
    Y extends Object declared in class C
    X extends Object declared in class B
  where CAP#1,CAP#2 are fresh type-variables:
    CAP#1 extends Object from capture of ?
    CAP#2 extends Object from capture of ?
1 error

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
interface A {}

abstract class B<X> {
    abstract X m();
}

abstract class C<Y> extends B<Y> {
    @Override
    abstract Y m();
}

class MyBug<Z extends C<?> & A> {}

---------- END SOURCE ----------