Constantly bonemealing weeping vines and then breaking part of the vine occasionally creates a new "sapling"

I'm working on a weeping vine farm in my testing world, and I've noticed that if a dispenser is constantly bonemealing weeping vines and if part of the vine is broken at any point, it has a chance to form a "sapling" instead of the regular plant part. This actually breaks the farm, because the vine can't grow anymore because it is blocked by the "sapling".

Steps to reproduce:

1. Set up an observer clock to power a dispenser which constantly bonemeals a weeping vine 
2. Break pieces of the vine in between the sapling and the ground
3. Notice that occasionally, a "sapling" forms.

 

I'm attaching a video so you can check this out for yourself.