I can see that both versions are used and typically we tend to use the hyphen-version for Korean names on TMDb. There was an edit war going on last year so a moderator must have decided that enough was enough. Anyhow, let's keep it open to see if another moderator think the other version is the way to go. Thanks for your report.

Per the most recent press material, the official name should be Bong Joon Ho. I have set it like that today. Closing topic.