Windows and domain suffix addition
1: it is valid
2: no. it is there to help you enter server names locally "short" or with partial domains.
2 in particular is the culprit here. This is a stack function checking all default prefixes. Normally this is a technical non-issue as your prefix will end at your server (as it is authoritateive for the internal domains) and thus never hit the internet. Load and traffic make no real difference either.