& yes, I would indeed consider this as a vanilla bug considering ye plan to support servers officially.
There is no way to unload a chunk manually, I am indeed sending the correct package, this bug has been reported and confirmed with Mojang staff privately yet there is no fix yet.
Still reproducible as of 1.1.1.1, only slightly better. The old chunks no longer display (well, they load out slowly) but the new chunks still don't visually render.