Import issues from US to Europe (Belgium)

[Kyo28]

The oddest thing happened the other day:

I had ordered some BR's from Second Spin (USA store) to Belgium, keeping the total under the taxable amount and got them without any expenses.

I did the same thing, this time with Amazon expedited international shipping (not Priority Courrier!), again keeping the amount under the taxable threshold and guess what? I get slapped with a 10 Euro forfait for administrative expenses at customs.

What happened? Do people from Belgium now have to pay a forfait even though there are no import fees to be levied, just because they check your package? Or is this caused by my choice of using Expedited Shipping instead of Standard Shipping?

This really boggles me and if possible, I'd like to avoid it in the future.