To be honest, I don’t know if that is normal behavior. I added my Harmony Hub using PaperUI. However, what happens when you replace host="HarmonyHub" with host="<the ip address of your harmony hub>"?
But based on what would openHAB know that it is the same HarmonyHub? To be able to determine that it is the same hub openHAB would need to do a reverse DNS lookup to find the hostname belonging to the IP address that it discovered. I don’t know if openHAB does that. If it doesn’t then it will be comparing ‘HarmonyHub’ with e.g. ‘192.168.0.123’ which are not the same, hence my suggestion to try using the IP address in the Thing file. Then ‘192.168.0.123’ would match ‘192.168.0.123’ and openHAB would know it’s the same Thing.