Check the Metabase log (Admin > Troubleshooting > Logs), when it fails to save.
After you’ve created tableA/B and added data, have you synced/scanned the database in Metabase? Admin > Databases > “Sync database schema now” and “Re-scan field values now”
The (7) should not make any difference. It’s just the display width. It’s still just int which 4-byte signed.