@omega That's right, if shutting down redis over and over again is saving old data into the dump file, then Redis itself is not shutting down properly.
Redis itself never persists anything into memory (or rather, it shouldn't) once it shuts down, it's all dumped to disk.
Are you sure it's stopped? Check ps aux | grep redis for any errant processes. What does the redis log file in /var/log say? Any errors when shutting down?