Have the steering head bearings ever been removed/replaced? If so, as Paul mentioned...perhaps they are not seated completely.
More likely, the upper triple clamp was not secured in the proper sequence after being loosened/removed. After adjusting the bearings (large spanner nut under the upper triple clamp) it is imperative that the center triple clamp nut (30 mm head) be tighteneded BEFORE tightening the fork pinch bolts. Not doing so will not lock the adjusting nut in place, and can/will distort the upper triple clamp.
Eddie