[ovirt-users] Sparsifying VM disk not working

Hello, i cannot get sparsifying to work in lastest oVirt 4.5.4 release (not that i have tried with a previous release) I have two Data domains connected to oVirt using iSCSI & NFS. I created 2 testvm's and 50GB thin provisioned qcow2 disks for each, made some temp files, remove them and tried to sparsify, but it does not work. Error i am getting is: Error while executing action: Cannot sparsify Virtual Disk. Sparsifying is not supported for QCOW2 disk testvm1_Disk1. In virtual disk options i have enable, Bootable, incremental back and for one of the images i enable discard for testing purposes. What am i doing wrong?