Jumping and flying? Huh? It shambled pretty quickly and silently after Rick. That's what zombies do in this show when you're not paying any attention. Rick's behavior is not what you would do if you knew the corpse to your back might suddenly come after you. (Not in a well-written show.) What was Rick thinking? "It probably won't resurrect while I have my back turned, so I don't have to worry. And even if it does, it won't move fast, so once again, I am safe to ignore it." Or was he so absorbed in Carl that he forgot? Was he so absorbed that he forgot the zombie could be a threat to Carl as well? How much more sense does that make? Sure, it's possible Rick knew (and, again, we'll find out in the next episode), but if that's the case, the scene's an even bigger mess.
I think its just as likely Rick didn't know and was looking at Shane with regret and sadness, trying to deal with what he had just done. Rick probably would have had his gun out at least (and he didn't) if he were waiting for Shane to come back, right?
And what's the explanation behind Carl not saying anything (which would have ended the threat just as quickly as Rick turned and fired his own gun, which he has a lot more practice using)? If Carl couldn't speak, he could point. Aside from his silence making the scene more dramatically ambiguous, and aside from things playing out this way so Rick and Carl both "kill" Shane the way Kirkmann and co. wanted... it doesn't make much sense. And again, neither does the headshot at that distance by an amateur.
But things that happen in TWD often make no sense.