I tend to agree with you on this.
Although older versions of the mbuf library didn't have this restriction for
RTE_LIBRTE_MBUF_DEBUG (which was only used in the header file, and thus
controllable for the application build), RTE_LIBRTE_MEMPOOL_DEBUG works as you
describe, so the same could be reasonably assumed about RTE_LIBRTE_MBUF_DEBUG.
Let's not consider it a bug.
I tend to agree with you on this. Although older versions of the mbuf library didn't have this restriction for RTE_LIBRTE_MBUF_DEBUG (which was only used in the header file, and thus controllable for the application build), RTE_LIBRTE_MEMPOOL_DEBUG works as you describe, so the same could be reasonably assumed about RTE_LIBRTE_MBUF_DEBUG. Let's not consider it a bug.