So,
Kudos to CDNN Investments!
CDNN agreed to exchange the magazine for another one. All I had to do (after contacting them) was send it back with a copy of the invoice and note. I had a replacement mag (at no charge) in a few days!

This one locked back 2 out of 3 1911's I tried it in. Unfortunately, the one it didn't lock back (ever) was the Colt in 40 which I need it to.

I switched out the Greider 10mm slide stop from my Dan Wesson and viola it locks back in the Colt. Hmm..
Looks pretty good on the Delta too. Actually the Colt #4 slide stop looks pretty good on the DW CBOB.

So, some thoughts.
-Try to find some full follower 40 mags. Maybe Colt, Mec-Gar, Kimber, Wilson?
-Replace the Colt #4 with a Greider or other 9/38Super/40/10mm stop
-Tweak the MTM and try to gets it to work (they were only $12.99)
-Just use 10mm mags.