The spots in line on the underside of the tubing is from water droplets caused by humidity and 'sweating' pipes. I've never seen them lead to leaking. But flux that is acid based, and left on the copper, eats holes in the tubing and provides an excellent place for bacteria to live; which have an acidic waste, and both cause pinholes in copper tubing. Non water soluble flux happens to be the second most common cause of pinholes in copper tubing. The first or most common cause is not reaming the end of tubing that has been cut off with tubing cutters which allows for erosion corrosion caused pinholes.
The white/gray residue is caused by water from 'sweating' corroding the solder; especially lead based solder.
Gary
Quality Water Associates