I have custom trees for every sapling type. But sometimes it seems to happen that any tiype of sapling (even those, which are 2x2) grow a tree that is only defined in the Sapling queue of the oak sapling.

I planted a birch sapling and an oak tree grew and another time i planted 4 darkoak saplings, one turned into an oak tree and the 3 saplings left just stayed there.

There is no mistake in the sapling queues, i checked them all.

okay, i made a mistake... the last sapling in the queues hadn't a chance of 100%