this is not really a hydrogen defect, but it does make jacksession unusable
when the 'connect to default output pair' is enabled this messes up the jack connections when you restore a jacksession

for example :
- open hydrogen and connect only the Left Audio out to the system Left audio IN (nothing connected to the Right output of Hydrogen)
- disable 'connect to default output'
- save the jack session
- close Hydrogen
- restore jack session
> Hydrogen starts and only the Left out is connected >> OK

if you do the same, but you enable 'connect to default output' you will see that both the Left and Right output of H2 are connected to the system output when you restore the jacksession

So there is really no valid usecase where you can save a hydrogen song via jacksession and have 'connect to default output' enabled
> the best solution would be to auto disable the 'connect to default output' whenever a song is saved via jacksession