I wouldn't discount a hardware problem just because a machine is new, and I wouldn't expect a software problem to be quite so specific, but computers have a habit of inventing new 'learning opportunities!. X-)
It might be worth checking you don't have "sticky keys" enabled under the accessability options, you should also make sure you have the right keyboard driver installed. Without an external keyboard port, that's probably the limit of what can be done, since you wouldn't normally use the Tab key so often in other software to find out whether it's consistent across software.
Maybe someone else has some ideas?