Not all images making the jump from iPhone to Photosream

This has more than likely been raised before, but I need to know why some images just will not get pushed from my iPhone to iCloud via Photostream.

The last couple of days I have been out & about and on each day I have taken approx 35 photos. When I get home, it sits around waiting for a while, then eventually, through the wi-fi, it starts to push the images to iCloud. However, out of say, 35 images, it might push just 30. But it won't be the last 5 that it misses, it will be random images throughout the 35.

This means I then have to upload the missing images (not easy if a lot of images are pretty similar) to Dropbox and add them manually - pain in the a*s.

There seems to be no reason for this. Is there a limit on how many images will upload at once? Why does it miss some and not others? Do you need to be plugged in to the mains and charging fro it to work properly? Or is this just another Apple glitch which will hopefully be resolved in the next iOS update??

Thanks.