Ahh, that's an odd one.
Transaction fee of -12.5 BTC

State reorganization underway for BTC. F2Pool is the mining pool submitting blocks from the early 2000's.
Yeah.. 1999 now..
Oddly, Block #501728 was also empty, small (0.285 kB), and mined a short while later:
Block# 501726 timestamp: 1514638520 transactions: 0001 size: 0.2 kB
Block# 501727 timestamp: 1514639163 transactions: 2230 size: 1064.42 kB
Block# 501728 timestamp: 1514639176 transactions: 0001 size: 0.285 kB
Block 501727 was mined 13 seconds before 501728 and contained a large # of transactions.
Curious: were there any other odd things going on in the time say hours before and after these blocks? A large increase in orphaned blocks by chance?