Incompatible static wildcard bounds

FULL PRODUCT VERSION :
java version "1.8.0_51"
Java(TM) SE Runtime Environment (build 1.8.0_51-b16)
Java HotSpot(TM) 64-Bit Server VM (build 25.51-b03, mixed mode)

A DESCRIPTION OF THE PROBLEM :
Attached example compiles with source 1.7, but not with source 1.8.
I don't know if it is legal according to JLS 1.7 or JLS 1.8. It seems however, that it should be.

Code compiles when wildcard
Interval<?> interval = (Interval<?>) object;
is replaced by raw
Interval interval = (Interval) object;

I'm aware that isValid could and should be instance method, Validator could be generic class and so on - but let's ignore that.

REGRESSION. Last worked in version 8u51


ERROR MESSAGES/STACK TRACES THAT OCCUR :
IntervalValidator.java:8: error: method isValid in class Interval<C#2> cannot be applied to given types;
                        if (!Interval.isValid(interval)) {
                                     ^
  required: Interval<C#1>
  found: Interval<CAP#1>
  reason: inference variable C#1 has incompatible bounds
    equality constraints: CAP#1
    upper bounds: Comparable<? super C#1>
  where C#1,C#2 are type-variables:
    C#1 extends Comparable<? super C#1> declared in method <C#1>isValid(Interval<C#1>)
    C#2 extends Comparable<? super C#2> declared in class Interval
  where CAP#1 is a fresh type-variable:
    CAP#1 extends Comparable<? super CAP#1> from capture of ?


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
// Interval.java

public class Interval<C extends Comparable<? super C>> {
public C lower;
public C upper;

public static <C extends Comparable<? super C>> boolean isValid(Interval<C> interval) {
return interval.lower.compareTo(interval.upper) <= 0;
}
}

// IntervalValidator.java

public class IntervalValidator implements Validator {
@Override
public void validate(Object object) {
if (object instanceof Interval) {
Interval<?> interval = (Interval<?>) object;
if (!Interval.isValid(interval)) {
throw new RuntimeException();
}
}
}
}

// Validator.java

public interface Validator {
void validate(Object object);
}

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