Large Oak trees cannot be prevented by block

Used to be able to stop large oak trees growing by putting a block (10 blocks) above the sapling. Now on the odd occasion a large oak tree will still grow, even if a block is above to limit the growth - and sometimes if it grows taller said block will be replaced by the trunk. This no longer works as it used to and this breaks Oak tree farms, universal tree farms etc. I've noticed this issue since 20w18a.