I doubt ESXi creates the snapshots like this, because it doesn't support this format. Maybe it's related to the template/image which was created using an older version (and needs to be upgraded. Please take a look at e.g. virtuallyGhetto: 2gbsparse Disk Format No Longer Working On ESXi 5.1 for details.
Did you check whether the files are in use, i.e. referenced in the VM's vmware.log file?
André