VM Hypervisor (VMware vSphere Hypervisor 5.5.0 Update 1) was set up with VMware-viclient-all-5.5.0-1618071 and migration of two VM comming from VMWorkstation 7.x was successful and everything was running fine.
For one out of the two VM's I created a snapshot to do some updates on the guest os. That worked as expected.
Then I got the hint that the VMware-viclient-all-5.5.0-1993072 could deal with VM Version 10. So I installed the new client.
Everything looks fine, no errors, no hint regarding versions ... but the client couldn't deal with VM Version 10. So what, I can use VMWorkstation for managing the VM's
Now I created a snapshot of the second VM on the EXi Host and in the logs I could find "successful" - so I did my Guest OS Updates.
But after the first reboot everything was lost - it looked like using non persistent disk.
The snaps where created - but just 1 MB big. I tried it several times - the VM works as you would expect working with non persistent disks.
Due to the fact that it has worked before I went backt to the Vsphere Client 1618071 - and now the snapshots are working fine.