Step 1: Clear the MAC-list.
Step 2: Add MAC addresses with short name. Result:
Step3: Delete one MAC "Galaxy S5"
Step4: Add removed MAC. Result:
The screen caps are from ASUS stock and not Merlin as the IP address column is missing. Please can you check what firmware you are running.
I can't duplicate the error on an AC68 using beta 2 and chrome browser.
I second recommendation to remove spaces as they are not valid in hostnames
http://en.m.wikipedia.org/wiki/Hostname