I replaced my old Bluetooth dongle (some shitty Asus 1.0 or 2.0) with a newer one (if anyone is interested) and all previous connected devices got deleted.
It's nothing serious I just reconnect them, but it might be a bug, or a feature.
Is it a bug or a feature with Bluetooth?
Sounds like neither a bug or a feature, just the way Bluetooth works. The devices were paired with the old dongle. Now you needed to pair them with the new one.
It makes sense I guess, still strange to me that it isn't paired with the software.
HolySoap The pairing process involves the MAC for both the host (dongle) and the client (device), as well as a few other device parameters and a shared security key. If either device is replaced, they must be re-paired in order for the connection to be re-established.
This is not entirely unlike establishing an SSH connection the first time with password authentication in order to install a public key which can be used later to authenticate directly.
This is different than say, WiFi, where only the client needs to keep track of the credentials for the access point. Though, further registration may be required when assigning IPs from the router on that network.