What I expected to happen:

Trees would only generate if their trunk is in the right biome, or in some cases some intermingling is allowed (forests - taiga - jungle)

What actually happened:

Some trees generated in the wrong biome.

This is not completely an issue between taiga and forest with nothing between, but across a river or a swamp tree halfway up the side of a mountain (completely in the biome) is a bit weird.

Seeds:

1128660967236217397 last 4 screenshots

7500019863313131354 first 2, (-157,99,-37)