DNS not resolving from certain locations

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http://serverfault.com – I have a few domains in a server with WHM, dns of both (ns1.iwanktube.com, ns2.iwanktube.com) works fine on iwanktube.com domain as i can resolve it from my location. However the new domains i mentioned, works from most locations (actually they seem to be propagated on most of the world), however it works few times a day from my ISP, and then it just stop resolving. DNS change for those domains has been added 1-2 weeks ago. Domains im mentioning: Party-tube.com freepornix.com Ideas? Thanks in advance. (HowTos)