Though manually configuring works, it would be even better if the ClearOS static reservation feature worked properly. This may be a regression as there was a period of updates where it seemed to be working okay but not for past several months. Several old threads exist on this problem.
When it was working I could only get it to do so by turning the device off after DHCP had allocated a dynamic IP and before changing that device to a different static IP through web admin. But that no longer works and new devices remain on the initial dynamic IP regardless.