What is the local db?
The used HSQL db is just a local file in a sub-folder of your branch folder on your disk.
This folder is NOT synced with Teamserver. Which means that when you commit this is not transfert and shared. Thus when creating another branchline, this database is not included.
What is a snapshot?
Creating a snapshot is like creating a backup. This backup is a zip of the local folder containing the DB file and document folder. This snapshot is synced with teamserver. Shared with other team members. And part of the files which are used when you create a new branch.
When is the snapshot used?
The snapshot is only used, when you don not have a local db file for your local branch deployment.
When deploying a local branch the following happens
If you have already a local db, but you want to use the snapshot.
What happened in your case?
multiple options
In all cases; whatever you do on the mainline will not reflect on a branch line. Unless you create a new snapshot in the mainline. Create a new branch line or merge the main with the existing branchline.
And you can hack a bit