I am not sure what you should do.
MLCAD does not prompt you when a sub-model has changed. But you can click the "Revert" button and it will reload everything from the disk, including any saved changes to sub-models. But then, MLCAD does not support multiple sessions.
Pov-Ray only prompts you about unsaved sub-models when you try to render the parent model.
P.S. I still think if you are going to allow multiple sessions per instance, you should show tabs for each session.
[edit]
I just installed the latest alpha. Which menu shows the list of sessions? I can't find it.
MLCAD does not prompt you when a sub-model has changed. But you can click the "Revert" button and it will reload everything from the disk, including any saved changes to sub-models. But then, MLCAD does not support multiple sessions.
Pov-Ray only prompts you about unsaved sub-models when you try to render the parent model.
P.S. I still think if you are going to allow multiple sessions per instance, you should show tabs for each session.
[edit]
I just installed the latest alpha. Which menu shows the list of sessions? I can't find it.