Have a Sig manufactured Sig 226 mag that won't lock back in either of my 226's on an empty mag.  Happens when I shoot and when I insert an empty mag on this specific mag.  The mag falls free from one of my Sig's but does not fall free from the other Sig.  It functions fine other than that.  Any idea on fixes?

I know that the "glossy" black magazines have a follower that is one billionth of an inch too short to consistently lock the slide back on newer P226.  Had this problem when we switched from P226 DA/SA to P226 DAK.  You could try switching to a newer follower, or just resign yourself that the slide will not lock back reliably....use it as a range magazine.

Sig Sauer said something about magazine manufacturer differences, sorry but it's been a while since I tackled this problem.  

New mag spring??

Probably order a new follower and spring and see if that does the trick.  I guess worse case scenario I have a designated range mag.  I didn't know if it could be an  incorrectly cut mag due to it not falling free.

My apologies Sir, reading is fundamental!  I did not see the part about it not falling free.  That is a red flag for me, I would definitely get a new spring and follower.  Mag falling free every time and locking the slide back on an empty mag are two "steps" of the function check that Sig Sauer teaches at their armored school.  

Another possibility that I have seen before is the magazine spring was put in backwards (back to front instead of front to back) during re-assembly of the magazine after cleaning.  I can attach pictures if you'd like if I am not explaining it good.