[libvirt] changing compat when create volume from volume via libvirt api

I'm use via php binding https://libvirt.org/html/libvirt-libvirt-storage.html#virStorageVolCreate... and see that image grows: image: new.qcow2 file format: qcow2 virtual size: 4.9G (5242880000 bytes) disk size: 854M cluster_size: 65536 Format specific information: compat: 0.10 refcount bits: 16 image: old.qcow2 file format: qcow2 virtual size: 4.9G (5242880000 bytes) disk size: 277M cluster_size: 65536 Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false Why libvirt create new image with different compat? -- Vasiliy Tolstov, e-mail: v.tolstov(a)selfip.ru