Study/DO: adding instances of subcomponents and saving only saves the current instance

When adding multiple instances of a DO/study sub-component, e.g. DO instances, clicking the save button on one of the instances only saves this specific instance, all the others one are lost. The other ones should be saved as well.
Other edited data is probably also lost.
-> There should be only one unified saved button that would be sticky and save everything

Reproduce the problem by adding multiple DO or study sub-component instances, editing more than one, and saving from one instance. Trace the instance save controls and the surrounding form or state handling; done means one sticky unified save action persists every instance and other edited data instead of losing changes.

Written by the indexing model from the issue text.