I personally do not find it particularly odd that IR wouldn't respond to JM 'screaming' at the creek. If she says she screamed, remember, that is her report of her behavior. If it did in fact happen that way, her version of 'screamed' may be much different than someone else's; she seems to be less outwardly emotional than lots of other people. I also just know people who get lost in their own world (especially when out in nature), who probably wouldn't have noticed JM's actions. Another possibility is that IR just didn't really care what was going on...he had no responsibility to anyone else there, and seeing JM freak out, he may have just said to himself that if it were his business someone would let him know what was going on.
I have always felt like IR could easily have been led to believe certain things about the trip based on the fact that he doesn't have kids, apparently lives alone and is basically only responsible for himself, and was not emotionally connected at all to JM or VK. Not being critical, but I know people who have no interest in children or no interest in children that aren't theirs, and people who have lived alone and done their own thing for so long, they seem disconnected from others around them. It would not surprise me if IR never saw Baby DeOrr at all, but completely believed he was on the trip.
Other than the fact that LE does not seem to buy the disappearance story, my biggest sticking point with the whole situation is their descriptions of the period just before the 911 call was made. After hearing TC describe in some detail her experience with finding out Baby DeOrr was missing, I went back and re-listened to every interview the parents have done that we have access to. Their own words (not their reported words) are that they 'immediately' called 911, they 'frantically' dialed 911, they searched for 20 minutes and as soon as it became clear the baby was gone they made the call. They never mention repeatedly calling TC, waiting for her to call back, and only then, because she told them to, calling 911.
TC's statement was that she went on break and noticed lots of missed calls. She worried it was about her dad. She called back, not getting through immediately, then finally talked to a hysterical JM. TC says she was not super worried about the baby because she knew the area and believed it to be very safe. She then says that when she got home, she headed up...she does not say she left work right away. Chelsea asked her if JM called TC before she called 911; TC replied 'That is true.' She said she asked JM if she had called 911, told her she needed to call 911, and that JM's next call was to 911.
Calling someone over and over, waiting for that person to call back, talking to them and explaining what is happening, discussing all the most likely scenerios and then calling 911 after that person suggests it is very different from realizing your son is missing and then immediately calling 911 IMO.