I've actually noticed this about UID2. UID2 is a bit too fragile to use for these cases. On the CTF server I've seen other players' and my own UID2 change several times over the past few months and I didn't even try to change my UID2. I'm aware of how it can be changed without the need to format/reinstall and let me tell you alot of these people are probably changing their UID2 without even knowing it. That's how fragile it is. UID1 is a better option for this specific use case in my opinion. Yes it can also be changed, but in most cases (not all) whoever changes it, is doing it on purpose.