A problem that goes back to the Win8 previews last year.
Just tested this out again - updating a user Start Screen by simply using Win8.1. (i.e. "smaller" titles) ... and then by simply doing a login to a Win8 RTM with the same user account (domain user connected to the cloud).
It fails again. The tiles disappears and flows out to the right because of the reflection for tiles and their layout across Windows editions and releases seems to remain unmanaged?
It's a bug with that needs fixing? If the algo for the Start Screen can not sort out the eixsting layout - it will not only flow those dangling tiles right but it also overwrites your layout in the cloud ... like a Start Screen refresh in part (redo your layout all over ... more or less). Unacceptable, if this issue remains without being dealt with.
This can also happen just taking a user from Win8 RTM to Win2012 RTM ... also during previews. With the upcoming changes to the Start Screen ... this problem is just getting more complex.