I assume this is not meant to be an easy way to get sacred oak saplings?

Latest BoP build: BiomesOPlenty-universal-1.6.4-1.1.3.281.jar

Created new BoP world, cheated in some palm and pine saplings, applied bone meal and then removed the wood (Tinker's Construct lumber axe) and waited for decay.

A few moments later and I started to get those sacred oak saplings rather than the expected palm and pine.

Also in build 290.

Another case: acacia leaves drop mangrove saplings.

Confirmed.