Hello Dan,
If I understand correctly you have 2 Ring Groups (RG), the 1st of which has certain extensions only and has a Ring All strategy and the 2nd has all the extensions (including those in the 1st RG) and also has a Ring All strategy. A call initially enters the 1st RG that has a timeout of 10 seconds, and when this is reached you have set it to forward the call to the 2nd RG.
If I have comprehended your setup correctly, there is indeed a small delay (1-2 seconds max) when the first RG reaches the timeout and until it transfers to the 2nd RG. The reason for this is that once no extensions answer within the given time, the PBX must send cancel requests to all the phones already ringing and then transfer the call, thus the delay, so if an extension from the 1st RG answers within these 1-2 seconds, the call will already be in the procedure of being transferred to the 2nd RG.
If this is the issue you are describing, it is no a glitch just a necessity. If this is not what you meant please clarify the situation and we will get back to you asap.