I think I found the solution:
I ran into this problem yesterday when I decided to restore my phone to factory settings. Unfortunately, this fix will require u to restore
The way I fixed it was when I restored the first time, i set it up through the pc tutorial thing that walks you through on how you want to set it up, what accounts you want to sync, and what you want your home screen/pages to be and look like. I did not have this before i restored because the lady at AT&T skipped the tutorial when we turned it on at the store.
After i restored, I was in the same boat as you, my home screen kept changing whenever i would restart my phone. i would leave it with 3 screens and when i restarted, it put 4 more on, increasing it to its max size (7) and the prev screen i had as the home one would be switched to a blank one that it created for me. BEYOND FRUSTRATING! I would change this 3-4 times to see if it repeated it once i restarted and it did.
So, (and here is the fix), i restored the phone again but SKIPPED THE PC SET UP tutorial. My phone is all set up and no more home screens changing.
Not sure why it does this, there must be a bug in the software that when you set it up with a pc, it locks in the number of screens you set it up with and if you try to alter it outside that program (simply rearranging them/deleting them on your phone), it'll reset it back to how you had it set up when you went through the pc tutorial. In my case, it was 7 screens that i finished the tutorial with instead of the 3 I wanted after i finished the tutorial.
I hope this makes sense as im writing quickly while at work. Essentially, restore your phone but do not use the pc walk through to set up your phone!
Let me know if this works.