Why isn't my timeline syncing on my Twitter?

For whatever reason whenever I switch from my Twitter app on my iPad and a few hours later turn on the same app on my iPhone the timeline doesn't sync. I've used both iCloud and Tweetmarker for this functionality. I've also tried Tweetbot, Tweetcaster, Twitterific and they'll do the same thing.
Any ideas about this?
Thanks for the help and suggestions
Bob

Are they supposed to do as you describe? I guess I've never expected it would...

They do if I happen to go from one device to the other in a relatively short time but a longer time causes this problem.