Missing opentelemetry-java SERVER span with nested span - Stack Overflow

I'm seeing some odd behavior with opentelemetry-java (via SmallRye OpenTelemetry). For some context, this is running in the WildFly application server, which integrates smallrye-opentelemtry for its otel support. In SR Otel, there is a ContainerRequestFilter/ContainerResponseFilter that implicitly adds a span to all incoming Jakarta REST requests. You can see that code here: .9.2/implementation/rest/src/main/java/io/smallrye/opentelemetry/implementation/rest/OpenTelemetryServerFilter.java

For a simple REST endpoint (e.g., something that just returns a String), we see the expected span created and exported. However, if the endpoint method creates a nested span, the span created by the filter is not exported. That method might look something like this:

    @GET
    @Produces(MediaType.TEXT_PLAIN)
    @Path("/test")
    public String testOpentelemetry(@QueryParam("question") String question) {
        Span span = tracer.spanBuilder("explicit span")
                .setAttribute("com.acme.string-key", "value")
                .startSpan();
        try { 
            String answer;
            try {
                span.setAttribute("com.acme.question", "question");
                span.addEvent(question);
                answer = question + " received";
                span.setStatus(StatusCode.OK);
            } catch (Exception e) {
                e.printStackTrace();
                span.recordException(e);
                span.setStatus(StatusCode.ERROR);
                answer = "My failure reason is:\n\n" + e.getMessage();
            }
            span.addEvent(answer);
            return answer;
        } finally {
            span.end();
        }
    }

(This is a simple test endpoint, so it's not supposed to make sense :)

If I debug the SdkSpan class, I can see endInternal(long endEpochNanos) called and the span being ending, but it's not ever exported. If I comment out the span-related code, the "implicit" span is again exported.

Is there something odd about explicit spans like this verses the SpanKind.SERVER created in the filter? What am I missing?