1. No states have any special meaning.
2. "Default state" is the one which is set on startup. Originally it was always the first, but that is not practical in some situations.
Note that current state is global ("Engine" state). You can check all current states of defined by you sets in the Overview tab.
That Engine state is changed in 2 cases:
1. when changed during execution in Logic mode, so on MIDI/OSC message (even looped back). So in corresponding control or in function called from such control.
2. when changed in Monitoring mode, so in Feedback control or in Logic control called as a function from feedback control, when corresponding Action has "Set Engine" and it is checked.
During "Monitor evaluation" mode, so actions in a logic control prior Monitor Action, any state changes are "local". In case monitor is triggered, Feedback actions are called in Monitoring mode.
Changes from corresponding "Monitor evaluation" are still there. Once Feedback is finished, all local changes are lost. Sets are reset to Engine state. There is special "Set from monitoring" option
to explicitly save current local state as Engine state.
Note that "Set Engine" flag has reversed meaning in "Monitor evaluation" mode, changes with that flag set are NOT executed. So, do not set this flags in Logic control actions which are not functions called from Monitors (or till you hit the case when that is useful during "Monitor evaluation"... but you probably never hit such case

)