Describe the bug
When I add trees to my worldpainter map, and then export it to MC, the saplings evolve into vanilla trees instead. I can plant dynamic trees manually though. Thus, when I create worlds in minecraft, the trees are dynamic. I tried to edit the .configs file to force vanilla saplings to become DT saplings. And it only worked if I plant it myself. At first I thought it was a problem with CubicChunks, but as I mentioned earlier when I create worlds in MC with the CubicChunks option enabled, the trees are dynamic.

Rendering Glitches
Are you using Optifine? Yes.

'm using forge 14.23.5.2768 for 1.12.2.

The option to force vanilla saplings to become DT saplings only occurs when the player physically plants the vanilla sapling by hand.

Edit: I did notice that there's a forge TerrainGen event for when a sapling grows into a tree. I might be able to leverage it to work how you're asking.