[t-3]

That sounds to me like some kind of retransmission error - a packet with a keystroke is being sent but the ack is not received so another packet is sent? I know nothing at all about if/how bluetooth actually manages reliability though, so could be unlikely or totally impossible.

[TickleSteve]

packets are sequenced, integrity checked and encrypted to prevent replay attacks so unlikely to be a simple "send packet again" issue. More likely a key debounce issue or driver issue.