Seems like your leaves are not derived from minecratf leaves like in other mods, because Passable Leaves doesn't modify them to be intangible.
Leaves from your mod are the only ones that stay solid.

note: if you want to test with that mod, make sure you get the unreleased build for 1.12.2 with the PR, not the 1.12.1 one, which doesn't work at all in 1.12.2.