RockTiki

Can confirm I'm seeing this in my snapshot world with the experiments turned on too.

03:00.0 VGA compatible controller: NVIDIA Corporation GM204 [GeForce GTX 970] (rev a1) (prog-if 00 [VGA controller])
Subsystem: eVga.com. Corp. Device 2974
Flags: bus master, fast devsel, latency 0, IRQ 38, NUMA node 0
Memory at fd000000 (32-bit, non-prefetchable) [size=16M]
Memory at c0000000 (64-bit, prefetchable) [size=256M]
Memory at d0000000 (64-bit, prefetchable) [size=32M]
I/O ports at d000 [size=128]
Expansion ROM at 000c0000 [disabled] [size=128K]
Capabilities: <access denied>
Kernel driver in use: nouveau
Kernel modules: nouveau

Also have this
03:00.0 VGA compatible controller: NVIDIA Corporation GM204 [GeForce GTX 970] (rev a1) (prog-if 00 [VGA controller])
Subsystem: eVga.com. Corp. Device 2974
Flags: bus master, fast devsel, latency 0, IRQ 38, NUMA node 0
Memory at fd000000 (32-bit, non-prefetchable) [size=16M]
Memory at c0000000 (64-bit, prefetchable) [size=256M]
Memory at d0000000 (64-bit, prefetchable) [size=32M]
I/O ports at d000 [size=128]
Expansion ROM at 000c0000 [disabled] [size=128K]
Capabilities: <access denied>
Kernel driver in use: nouveau
Kernel modules: nouveau

tested in 1.14.4 release and issue is now resolved. This ticket can be closed. Not sure exactly when it got fixed, but am very happy my XP/bone farm farm works again.

A suggestion, limit it to projectiles coming from a player? not mobs or dispensers? Interested in seeing what the devs think. Certainly a bug for dispensers to be able to shoot arrows through obsidian like that. Also confirmed this affects firecharges and fireworks

Confirmed your results using 1.13 pre1. 

Dark Forests are also affected. Jungles are so dense they are basically impassible/unsearchable now, and dark forests aren't far behind. This density combined with MC122428 (fire spread to high) has made at least one of my worlds unusable because of a lightning strike, in the jungle, the resulting fire is just too much for the game engine and it crashes.

I'd really like to see this fixed, but in the meantime I have found another semi-workaround that I don't believe I've seen mentioned here yet. Minecarts that are dispensed onto the rails with a dispenser while the mob is standing on the block, do pick up the mob. For me this solves moving villagers around as I can herd them easily into a minecart loading spot. It still doesn't help me with other uses like my overworld enderman farm design which was able to work in 1.8, and is now just is broken completely because of this bug, and possibly also the bugs that @Scott R. Godin is talking about with activator rails, which ya can't really test on scale till this is fixed.