I often experience the same situation with my gelding, Cody. It least we know that they love their jobs, right? My horse is pretty funny when it comes to jumping, he will and can jump anything that you put in front of him, depending on his mood. If he is in a really great, excited mood, he'll jump all the obstacles in the ring, flawlessly. Now, if he feels antsy, or irritable, he will rush the jumps, and he will refuse the ones he doesn't rush. When he refuses, he is REALLY tricky about it. He has the speed going, and he acts just like he is going to jump it. So, you loosen up on the reins and believe that he will soar right over...right? WRONG. At the last minute, he bolts off to the left. It's enough to send the inexperienced rider over his neck, luckily, I've adapted quite well and have minimized my falling experiences.
I have never met your horse in person, and you didn't provide much information about him. However, I can tell you this much. The majority of horses tend to get "worked up" or "excited" right before they jump. They will lunge forward at the last second, sometimes leaving you unprepared, to jump. The easiest way to break them of this habit, is simply to tire them out. If you think that your horse is starting to rush, make a circle, don't be afraid, show him that it is NOT acceptable. Also, prior to jumping make sure that you do plenty of cavalettis and trotting in circles, such as figure eights or the likes. This will exhaust him and he will be much better behaved when you jump!
Try hard NOT to overwork him, though. Just tire him out enough where he becomes submissive and will respond to your aids.