Front of bike (headset or suspension) doesn't feel right

[matthewslack]

Two other sources of movement, although should not be present on a new bike:

Slightly loose disc mounting bolts, or worn centre lock splines.

Inadequate spoke tension allowing a few degrees of 'wind up' under braking.

I've had both on my front wheel, the first mileage related and the second when I rebuilt wheel without enough tension.