DNS local name vs public name

I have a server, lets call is servername.

Now servername is technically servername.domainname.net

Now servername is also a web server that has a subdomain setup the based off the full machine nameservername.domainname.net

When accessing servername via http://servername from inside our organization all works fine.

When accessing servename via http://servername.domainname.net from inside our organization its a 50/50 on if the end user can access it.

When accessing it from outside via servername.domainname.net it works 100%

When a user is not able to access servername.domainname.net they can not even ping it or traceroute it, all come back unresolved, but if they try pinging or tracerouteservername it resolves.

any ideas why it will not resolve internal for via full name ?

in dns I have a A record for servename that registers as servename.domainname.net