Everytime I reboot the device, the actual amount of data for today is saved under yesterday's row... yesterday's abount is saved under day before's one, and so on.
Maybe a couple of screenshots are more clear.


Difference between two screenshots is that one has been taken before reboot and other after reboot.
Date has not changed between reboots.
Where you see 4.6 Gbytes (24th Oct) is actually the usage at my 1st reboot today.
Then I consumed 2.9 Gbytes more, and rebooted again.
Then 2.8 Gbytes and rebooted.
Then 2.8 Gbytes and rebooted.
etc.
Where you see 59 Mbyte, 0 kBytes and 21.044 Mbytes is actually 3 days ago (Fri), day before yesterday (Sat) and yesterday (Sun), because I left home on Friday, been out until Sunday late evening.
Can somebody explain what happened, and maybe how to fix that?