LeClercus - greetings - I do not see anything odd in the fuel figures. I suspect a little language confusion there.
Note that 10:10:14 [2nd Pilot] "Approximately 11 tonnes for landing" is estimated fuel after landing at Smolensk
10:18:24 [2nd Pilot] "We have approximately 13- 12,5 tonnes" would, I expect be the fuel figure on board at the time..
10:23:55 [Capitan] "11 tonnes remaining" - I believe to be estimated on landing for ATC benefit
10:33:25 [Flight Engineer] "Currently we have 12 tonnes" is 15 minutes after12.5 -13 tonnes is reported on board and is about right - to have burnt around .5 -1 Tonne (2-4 tonnes per hour)