AD9516-4 eval board holdover not working

We are using a AD9516-4 eval board as is (no hardware change) where we have implemented a PLL circuit. The PLL is working, the software says that is locked by looking at the Config PLL section. Now we would like to test the holdover functionality, we don't want an automatic reference switchover. In the Config PLL section we have set "enable holdover" flag but when we remove the reference signal, the charge pump is not put in high impedance and there is no sign of holdover functionality (the DLD bit shows the unlock but the holdover bit is not enabled).