smbget -U DOMAIN\user and smbget -U user@realm is not supported. Patch will follow.
This bug was referenced in samba master: acf259c7e0b81b2b178d467102ced7826c109036 badbbceb76f41ddb86481ffd02f06f197258c1cb 9c76563ba2460187bbfc2e2c75e9237b82357139 1104916d227550f7c445e61d8ee3b62983c052c4 d81acef3924ef1484e3e0467e6441f4792c84f3d 1f3f88603a40e11cf1c9326a1f16d27e0d9337e1 0e07d0ac220226306c10f39dad1031382264d4e4