What version of Data Protector are you running?
I'm not sure what might be causing this, but, perhaps, you may have duplicate entries in the 'cell_info' file where the hostnames are kept, except one may be a short name ,and one may be fully-qualified
If you pick a particular file from "C: [servername.domain [C]]", right-click on it, and pick REstore Version, then, do teh same for "C: [C:]" are you seeing the same Restore Versions for both?
Usually, this indicate that some backup specification may have the Fully-qualified name, and the other does not, but, my feeling is that you would not see teh same Restore Versions for each