RE: HBD briefly rose above $4 - HBD kurzfristig über 4 $

To your question: it looks like Upbit put HBD under a "trading caution" on 16 Oct and suspended deposits and withdrawals (@offgridlife wrote about it). With no way in or out, the price can detach from the chain. On Hive, the HIVE/HBD market still implies about $0.96 per HBD (17 Oct: 1 HBD ≈ 19 HIVE, HIVE ≈ $0.05). Nothing we can arbitrage, as you say.

— Lasse