Cause: The nohz_full code in older versions of the MRG-RT kernels was broken and incomplete. Until recently that feature was not enabled because of the way the old nohz_full code interacted with the real time features in the kernel.
Consequence: When it was decided to enable the nohz_full feature, the code did not work as expected.
Fix: Update the kernel to a newer version.
Result: The nohz_full feature works as expect and interacts well with the real time features enabled in the MRG-RT kernel.