Mag pops out

[RWGARLOCK]

Hi, I am a new member, and would like to know if anyone else has had this problem with a Walther PPK/S 380.
With a full magazine ( 7), and one in the chamber, the magazine, almost always, pops out on the first trigger pull (DA). The first round from the magazine never makes it into the chamber.
After reloading that round back into the magazine, and reinserting the mag, and racking the slide it works
most of the time through the rest of the load in the mag.
If I cock the hammer myself, on the first shot, (SA) with a full mag and one in the chamber, then things work 90% of the times.
My thumb is not near the mag release to depress it by accident.
I have tried 12 different brands of ammo, all the same.
A gunsmith has not taken the gun apart, but thinks the mag catch is good and tight.
Once the mag holds in there, after 1st shot, no problem.
I did read that new magazines ( I have 5 new, 2 old) need to be broken-in????
The PPK/S is from Interarms I bought used 6 months ago. Problem started soon after.
Another thought---Could too much slide lubrication be getting around the catch and letting it release with
the DA pull, and the shock from the first round going off.
Any ideas before I take it in for repairs, and wait and wait for parts from S&W.
Thanks
RWGARLOCK