This is fixed in the current maintenance release (BIND 9.10.6. Released 2017-07-28).   Your OS is three maintenance releases behind the current release (BIND 9.10.3  Released 2015-09-16).  I suggest that you open a bug report with them requesting that they integrate the current maintenance release.

4588.   [bug]           nsupdate could send queries for TKEY to the wrong
                        server when using GSSAPI. Thanks to Tomas Hozza.
                        [RT #39893]