tracktype grade 1 not considered as paved?

I've made the observation that tracks with tracktype=grade1 are avoided in 'paved only' routing mode? Is this by design?

The wiki defines it as 'Solid. Usually a paved or sealed surface.'

At least in Germany grade1 is normally paved and perfectly usage with a road bike.

Do additional properties like surface/smoothness help to select it for paved routing?