ING Mortgage in principle referred to underwriters

Hello,

Im a first time buyer try to get a mortgage with my girlfriend for 75% LTV. I had an AIP with Leeds BS but their rates have change since applying so I went to get a mortgage with ING, and its gone straight to the underwriters at the decision in principle stage. Is this normal?

We both have good credit history, no debt, I just missed a card payment once about 2 years ago.