ADDITIONAL SYSTEM INFORMATION :
The has been reproduced on openjdk-8u232-b09 on Windows 10, openjdk-11.0.3 on Ubuntu 18.04 and openjdk-11.0.2 on Windows 10.

A DESCRIPTION OF THE PROBLEM :
According to the documentation on CompletableFuture.whenComplete(), this method "Returns a new CompletionStage with the same result or exception as this stage". However, subsequent invocations of whenComplete() provide a different exception. It has been wrapped in a CompletionException.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
The following test case produces two different stack traces for each of the whenComplete invocations:

    @Test
    public void testWhenCompleteKeepExceptionalResultIntact() {
        RuntimeException expected = new RuntimeException("original");

        CompletableFuture<?> result = new CompletableFuture<>();
        result.whenComplete((r, e) -> System.out.println(e.toString()))
               .whenComplete((r, e) -> System.out.println(e.toString()));
        result.completeExceptionally(expected);
    }

    @Test
    public void testThenApplyKeepExceptionalResultIntact() {
        RuntimeException expected = new RuntimeException("original");

        CompletableFuture<?> result = new CompletableFuture<>();
        result.thenApply(e -> e)
               .whenComplete((r, e) -> System.out.println(e.toString()));
        result.completeExceptionally(expected);
    }

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
For the first testcase (with whenComplete):
java.lang.RuntimeException: original
java.lang.RuntimeException: original

For the second test (with thenApply)
java.lang.RuntimeException: original
ACTUAL -
For the first testcase (with whenComplete):
java.lang.RuntimeException: original
java.util.concurrent.CompletionException: java.lang.RuntimeException: original

For the second test (with thenApply)
java.util.concurrent.CompletionException: java.lang.RuntimeException: original

FREQUENCY : always