Does it achieve slidelock with other magazines? Does this magazine exhibit the same behavior with other 39-series pistols?
From the photos it looks like the mag body is out of spec, or the slide stop is out of spec, but would need to show them next to the same parts from other 39s to see for sure.
I think we need to know about what your other magazines do with this same gun, and what this magazine does with other 39 series pistols.