I've been having this problem with my launchers lately. Whenever I press the back button to close an app and finally go to the launcher or just press the Home button, I've noticed that the launcher restarts itself (no, it doesn't force close, just restart) all the icons and widgets start to appear gradually, it's really slow and it kinda get's on my nerves. This happens 8/10 times.
I first noticed it while I was using the Xperia Active launcher, same thing happened with arc and LP. What causes this to happen? Low RAM maybe?