With the companies I am familiar with who form fasteners like that while I would say that I would believe the cracking to be common, the more correct question would be- how did it get past QC and out into the hands of the public?  Common as part of the manufacturing process does not mean it should have gotten boxed for sale.

As to rather it is a concern, that all depends upon the intended application.  It is obviously weaker through an area that will be subject to stress in the tightening procedure.  If it comes apart while tightening, it will be even more difficult to remove. 

Personally, I would not use it.

Have a Great Day,  Brent

Bill, I believe that if you contact the bolt mfg you will find that it may very well be an acceptable bolt. I have run into batches of TC bolts that have these "bursts" in the head of them. I contacted the bolt mfg and they gave me the acceptance criteria(don't remember the ASTM#). I sent them a sample of what I had found and all of the samples that I sent met the acceptance criteria. I didn't use some of these that were questionable to me because I didn't want anyone to see them and raise questions about them even though they may have been OK to use.
EDIT*
Found the ASTM F788 specifies the acceptable/rejectable surface discontinuities of bolts/nuts

Back in the "good old days" when Standard Pressed Steel and other respectable companies made socket head cap screws here in the rust belt of the USA, the top of the head was faced off [just like a facing operation on a lathe] after forming. This operation would have removed most if not all of the material in question, and leaves the socket walls true all the way to the face.