This has to do with the flash being optimized to illuminate subjects probably ~5ft away (mostly people at parties, etc). It's not a dedicated macro camera, and you can't direct the beam or increase the light cone, so it's directing the light past the image area of the lens when you have it very close to your subject (essentially creating a very bright hotspot far off to the right of the area you can capture at the MFD). I can think of two solutions to this.
1. Get a pocket flashlight and illuminate the area manually
2. Back up a bit, shoot the serials/vins/etc and then do a center crop. The camera in Lumia is good enough to product legible text in a small portion of the sensor. (edit) - Make sure you get the numbers as close to the center of the frame as possible - I've noticed a lot of sharpness falloff toward the edges of the frame.