Apps can't see some photos in camera roll

I'm adding some slides to a keynote deck and grabbed a few images from the Internet for this. I can see them in my camera roll:

The last three pictures, encircled in red, were just saved to the camera roll within the last hour - and all within a few minutes of each other.

But when I try to call up the camera roll from within Keynote, here is what I'm offered:

You can see the last picture is the same as what's on the camera roll, but the 2nd and 3rd from last pics on the camera roll don't appear here, so I can't add them to my presentation.

I opened File Browser, and it too cannot see the same two pictures:

Since File Browser allows me to see the file names, I notice that there's a gap between IMG_4839 and IMG_4844. Four files seem to be missing. I checked the 'recently deleted' album to make sure I hadn't recently deleted anything to account for the gap in file names. Nothing was there.

I went back to the camera roll to see if I could spot anything unusual about the two "missing" pictures. That's when I noticed both of them got time-stamped "December 14, 2009 at 5:48 PM", even though I just saved them today:

That leads me to believe that Keynote, and other apps that can access the camera roll, are listing the files in chronological order, according to the incorrect time stamp. That means the "missing" pictures are there, but I'd need to scroll waaaaaaaaaaaaaaaaaaay back to find them. It's nearly impossible to do this in Keynote since the thumbnails aren't dated. I went to that date range in File Browser and sure enough, there they were:

Funnily enough, I noticed some photos were time stamped 2005, 2003 and even one got a 1970 time stamp! See for yourself:

It looks like the iPad is (sometimes) reading the photo's birth date from the EXIF data rather than simply applying the current time stamp when I save the picture to the camera roll.