Hi Barefoot, it doesn't seems to be the 11GB causing the problem because I did the same test with 28GB free on the HDD and the results were exactly the same except the shadow storage capacities. I got the same 4 restore points. During the fifth one the shadow storage space was deleted with the volsnap eventid 25 in the system event log.
At that time the used shadow copy storage was something above 393.422MB
The allocated storage 1.785GB
There was no Vssmax limit (unbounded).
Now that there is 28GB free I will again upgrade/repair windows 7 because during the previous attempts there never has been so much free space. Perhaps this repair will fix the problem as it was mentioned in other threads.