When importing a user into a Mostro instance other than the default one, the user is restored correctly, but after closing and reopening the app, the selected instance does not persist.

Steps to reproduce:
1- Switch to a different Mostro instance (if you close and reopen the app at this point, the instance does persist).
2- Import a user into this instance (the user is imported correctly).
3- Close the app.
4- Reopen the app.

Expected behavior:
The app should keep using the previously selected Mostro instance.

Actual behavior:
The imported user is present, but the app falls back to the default Mostro instance.
If the user manually selects the other instance again, it then persists correctly.

Note: This bug is already present in version 1.6.0; it is not new to the main branch.