clone_kernel test fails on Intel(R) Gen9 HD Graphics NEO

[Francesco Giacomini]

The clone_kernel test (in test/test_kernel.cpp)

BOOST_AUTO_TEST_CASE(clone_kernel)
{
    REQUIRES_OPENCL_PLATFORM_VERSION(2, 1);

    compute::kernel k1 = compute::kernel::create_with_source(
        "__kernel void test(__global int * x) { x[get_global_id(0)] = get_global_id(0); }",
        "test", context
    );

    compute::buffer x(context, 5 * sizeof(compute::int_));
    k1.set_arg(0, x);

    // Clone k1 kernel
    compute::kernel k2 = k1.clone();
    // After clone k2 0th argument (__global float * x) should be set,
    // so we should be able to enqueue k2 kernel without problems
    queue.enqueue_1d_range_kernel(k2, 0, x.size() / sizeof(compute::int_), 0).wait();
}

fails when run on my laptop's GPU (Intel(R) Gen9 HD Graphics NEO).
The error message is:

.../Downloads/boost.compute.git/include/boost/compute/command_queue.hpp(1428): fatal error: in "boost::compute::event boost::compute::command_queue::enqueue_nd_range_kernel(const boost::compute::kernel&, size_t, const size_t*, const size_t*, const size_t*, const boost::compute::wait_list&)": boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::compute::opencl_error> >: Invalid Kernel Arguments
.../Downloads/boost.compute.git/test/test_kernel.cpp(315): last checkpoint: "clone_kernel" test entry

*** 1 failure is detected in the test module "TestKernel"

If I set explicitly the argument after cloning:

k2.set_arg(0, x);

the test is successful, but this is exactly what the test is supposed to check.
I thought the problem could be with the underlying OpenCL library, but the attached program, written directly using OpenCL and hopefully reproducing the test, doesn't fail.

Any idea? thanks.