The dates in TGDB are all consistent, yes, but the way these are interpreted by The LaunchBox may differ depending on the local user's locale settings, unless the code overrides these settings, of course. Anyway, it's just an idea.
I get this too. Being a software engineer myself, I'd hazard a guess it's a date conversion problem. All the ones which work can be interpreted as either a DD/MM/YYYY or MM/DD/YYYY date format (although obviously the former would result in an incorrect date conversion), whereas the failing 09/19/2005 example can only be interpreted using a MM/DD/YYYY format.