When you use item shadowing in a block and try to place it with the mod installed the block does not change its status (it does not refill, i have the other shadowed item connected to a shulker unloader) until i use a rocket from the left hand or i drop a single item.

So do you still have this issue? Because in my testing this didn't happen neither in Singleplayer nor on servers. It might also be an incompatibility with another mod