Opening Elf Town in 1.6.0.0 RC0, Beta 15 causes an assertion (BlockLegacy::getBlockState)

Verification builds: 1.6.0.0 - RC0, Beta 15 (980905)

Summary: Opening Elf Town in 1.6.0.3 RC0 Beta 15 causes an assertion (BlockLegacy::getBlockState).

Impact: An assertion appears as soon as the world loads.

Repro Steps:

1. Open Elf Town

Observed Results: An assertion appears and the game client completely freezes.

Expected Results: An assertion should not appear.

Screenshots/Videos attached: https://i.imgur.com/CTD6kKN.png