You probably have your 'Use burst cooldowns at X%' set to high, if you set that to say 90%, then it would use it when your target is at 90% health.
Also Richie, to your above comment, yes it does use Heroic Leap and Charge at the same time, almost every time for me. I just disabled the Use Heroic Leap as gap closer option and manually do it, but still it is a bug with it, just to clarify.
I can't believe it until you show me a log where it happens
