Six Flags Entertainment Corp. is finding that junk-bond investors, basking in a record rally that has generated bigger returns than stocks the past four years, have short memories.

Two years after emerging from bankruptcy, the operator of such amusement parks as Six Flags Magic Mountain in California and Six Flags Great Adventure in New Jersey, may use more than half the proceeds from an $800 million note sale to buy back stock. Six Flags leverage ratio will rise to 3.6 times from 2, according to independent debt research firm Gimme Credit LLC