Tree falled - Planted saplings sometimes grow as fallen trees

^{Update by [Mojang] Mega_Spud (Jay Wells):}
Summary:
Trees grown from saplings can sometimes grow as a fallen tree variant.

Steps to Reproduce:

1. Start a new flat world
2. Walk along and repeatedly use the command /fill ~ ~ ~ ~100 ~ ~ sapling to plant several rows of saplings
3. Wait for the rows of saplings to grow (Increase random tick to speed up repro)

Observed Results:
Eventually some will generate as fallen trees, or just as a one block stump.

Expected Results:
Fallen trees should not grow from saplings.

Screenshots/Videos attached: Yes

Notes:

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Original Description:
What the heck mojang..Is this supposed happend?? After a few min,It grow and falled..