If define nested model, that is correctly loads nested data from BE, then save it with
PHP Code:
writer: {    
allDataOptions: {

partialDataOptions: {

configuration it saves all nested data as expected.

BUT looks like it ignores BE response data, that is bad especially for creating new models where response often contains additional data that is not present in model (most important id of cause).
Also nested stores stay "dirty" (their models) if they was modified before save.

So far I see that model.getProxy().getReader().readAssociated() is not called after save and raw response nested data stay in model.data
if after save call model.getProxy().getReader().readAssociated(model, model.data) nested data from model.data are removed and associations are created/updated like in normal load process.

Does anyone know, is there a way to get updates from response automatically, maybe it's configurable?