[CentOS] kpartx can not detach

OS: EL6 - sometimes I use 

kpartx -a /mnt/.../lvdisk.img 

to map the partitions and mount them via 

/dev/mapper/loop0pX

After using the disk (unmounting it) I noticed that 
detaching such mapping via kpartx -d does not result 
in freeing up the loop devices. Results: System reboots 
shows that the filesystem where lvdisk.img is located 
can't be unmounted. 

lsof, fuser, ps does not show any usage. Even removing the 
device node via 

dmsetup remove /dev/mapper/loop0pX

does not help. Trying to unmount the underlying filesystem 
still shows /mnt: device is busy.

Any other suggestions would be greatly appreciated!



--
Thanks
LF