Evidence of a warped build plate? The first layer is very patchy indeed.  I've calibrated the build plate pretty accurately but even if it was a badly calibrated build plate I don't think it would have this effect.



It doesn't seem to have a negative effect on the print.


Should I be concerned about this? 
Is this due to a the build plate fault?
It looks like your first layer is way too close to the bed. The printer is trying to squash the plastic down very thinly, resulting in inconsistent extrusion. You will likely see better results if you move the nozzle away from the bed a little bit. Increasing the thickness of the first layer might help as well (this is a setting in your slicer).

Keep in mind that if you're trying to print (e.g.) a first layer with a thickness of 0.05mm then a 0.025mm variation in the height of the build plate will result in very strong variation in the thickness of the extrusion on the first layer; in some places it will only be half as thick as in other places. If instead you used a 0.2mm first layer, then the 0.025mm variation barely makes a difference.