Yes, that’s definitely strange. You mean you’re seeing channel release due to “radio lin messages” ? That’s on the A interface ?
In other words : are you sure that you “DCR” is counting only TCH drops ?
On the other hands, a non-response from the HLR might lead to a radio link failure.. If an internal MS timer expires, the Ms will end the connection, and the BTS will detect a radio link failure (MS not alive anymore) … but I’m really not sure.
And finally : is there a Siemens feature that would trigger the authentication during the TCH, rather than the SDCCH ? If such a feature exists, that might explain your observation.