Sorry but you are mistaken. I haven’t had time to get back to this post and the OP for a while, but I need to clarify this…
Snapshots ARE independent sessions. In all honesty a snapshot is a complete session file in itself.
Where the confusion I suspect is happening, is that when you create a snapshot file, it does not automatically switch to that snapshot, anything you save will continue to be saved in the original, UNTIL you EXPLICITLY open the snapshot file. At which point if you have unsaved changes you will be asked if you want to save them or not. All of this I just doubly confirmed a moment ago.
I other words, if you create a session, named SESSION. Then you work on this session and create a snapshot of the session, named SNAPSHOT. If you then continue working, and press SAVE you will save over the SESSION file, NOT the SNAPSHOT file.
If you do some changes to SESSION, and then try to open SNAPSHOT, you will be asked if you want to save your changes to SESSION first, as otherwise your changes will be lost.
If you open SNAPSHOT and then do some work and press save, you will save over SNAPSHOT. SESSION on the other hand will be untouched.
The only time I can think of that this is not strictly true is when dealing with embedded files that are not copied to the session, as updating those files will update across the board as the file itself has changed on disc, and session files only point to the source files with regions. However most people are importing the files(Copying the files to the session) and this is not an issue for them.
Hmm your first post there is very odd indeed. It doesn’t sound like you removed the first portion of the file in either session, so I can’t think of a reason it would be gone, unless maybe you just didn’t see it as you moved the start marker or something of that nature. I still don’t have time to look in depth into this yet, but I will try to come back to this in a few days when hopefully I get some sleep again.
I will say however, that as long as I explicitly open the snapshot, the original session remains unchanged, and I confirmed this as well before posting.