Hello Renatas,
I'm not sure that 'you must always use Transaction TPM18'.
There are two case of derived flows:
1) as we discussed above
2) derived flows for position outflows, calculated in transaction of security disposal (example - DBT_E001). Such flows are calculated automatically (with 'online' mode) and posted when you posts transaction of security disposal in TBB1. So in this case we don't need to use tpm18.
I guess the reason of such behaviour is:
1) base flow for HAC_B014 isn't fixed in TBB1 so the derived flow isn't posted too
2) base flow for DBT_E001 is posted in TBB1 so the derived flow is posted together with it.
What do you think ?