Tungsten 4+ ion magnetism?

I just had a quiz and struggled on a particular question:

Tungsten forms a $+4$ ion. It is observed to be diamagnetic. The electron configuration for this ion may not be what you would expect. Write the electron configuration for tungsten(IV) that is diamagnetic.

So if tungsten has a configuration of $\ce{[Xe] 6s^1 4f^{14} 5d^5}$ and it loses 4 electrons wouldn't it be $\ce{[Xe] 6s^0 4f^1^4 5d^2}$? And this would be paramagnetic since there are 2 unpaired electrons in the 5d subshell. How could it be diamagnetic?

• Now here’s a hint: ‘The electronic configuration for this ion may not be what you would expect.’ – Jan Jan 25 '16 at 22:32
• Maybe the energy difference between 6s and 5d orbitals is very low, leading to a more stable configuration 6s2 (occupied sub-shell). – Orr22 Jan 26 '16 at 11:15
• Oddly the NIST database for atomic spectra suggests that the $\ce{W^{4+}}$ ion has the configuration $\mathrm{[Xe](4f)^{14}(5d)^2 }$ and a triplet ground state, which would make it paramagnetic after all. – Nicolau Saker Neto Jan 29 '16 at 11:35