This problem could be caused by the surface tension of the oak. Surface Tension, sometimes created by sanding, can cause stains to not adhere to the grain of the wood.

You have a few options:

1. Lightly hand-apply the first coat, then spray (without wiping) a second coat.
2. Hand-apply stain the first coat. Then tone the piece by applying a mix of 10-15% stain with topcoat.