The title says it all! The game refuses to pull items through blocks. I discovered this issue when I was modifying my mob farm, so I could toggle between automatic and XP farming. I put magma blocks over the hoppers, then, while trying to step forward, accidentally hit the Q key. The items dropped but were not sucked into my hopper system! Screenshot attached. I must say, if this is a new feature, it sure makes automatic mob farms harder.