Yes, it's REALLY important that after each use, you 'flush' (press the flush plunger to enable the bag and contents to drop into the incineration chamber) and then press the appropriate button (the incinerate button on the BASIC and either 'small/urine' or 'large/faeces' on the FAMILY).
If you don't press the incineration program, there is a good chance that the contents will not be fully incinerated.