Why cannot I ping computer name without dot?
You probably do not have a WINS server on the network. Windows first tries WINS server for single part names, because it assumes that these are NetBIOS names and when it fails it does not try DNS.
According to Resolving names article, WINS is the first thing to check, however a subsequent step are supposed to make a DNS query. It's possible that since this particular article does not go into a lot of details, there are some conditions that are being met, that aborts the resolution process before it reaches the DNS step.
This is a longer article on the subject.