Fuel consomption vs simbrief profile

Something I've now noticed that could also be part of the problem (illustrated with an example): the flight plan in the FMS is fully populated (F-PLN page), but no step climbs have been entered yet. The aircraft is fueled. On the FUEL/PAYLOAD page, the planned ZFW and ZFWCG as well as the block fuel are entered. In the fuel section of that page, trip fuel shows 70 t and an EET of 06:10. The same values appear in the footer of the F-PLN page. The SimBrief flight plan shows a trip fuel of 67 t and an EET of 06:02.

Now I insert the step climbs, and both the FUEL page and the F-PLN page show almost the same values as the SimBrief plan. So far, so good.

However, here is a procedure that causes a discrepancy: if, in addition to the step climbs, I also enter an estimated time of departure in the flight plan and then insert both into the plan at the same time, the FUEL page suddenly shows a trip fuel of 72 t and an EET of 07:22. That's suddenly 80 minutes more flight time. Strangely, the F-PLN footer correspondingly shows insufficient arrival fuel, but the EET there still works out to just over 6 hours.

If the step climbs and the estimated time of departure are inserted separately, i.e. not in a single step, the problem doesn't occur, or at least it didn't in my case (tested only once so far).