Tested dark oak saplings acquired through all known means (/give, Creative Inventory and through direct dark oak leaf drops) on both naturally generated and manually placed dirt and grass, both in sunlight and not, with all appropriate requirements met. Saplings will not grow, even with enhanced tickrate gamerule or with copious amounts of bone meal.

Have also tested 1x1 (alongside the normal 2x2) setup of dark oak sapling in case of unannounced change to dark oak mechanics, with no success.

Reproducible with ease, simply use any dark oak saplings as would normally be intended; they will never grow.

All tested in single player only.