The issue is; when carrying on the left side using a soft holster, thin/soft leather or fabric, is that you unknowingly bump into "stuff" that will activate the mag release! The cure is to use a holster that protects the mag release, with kydex being one of the better choices!
I found the cause at one of my jobs where I had to navigate around a bunch of desks, they were just the right height to bump into my pocket carried pistol. The bump was light but hit just the right spot.
I would not recommend shortening the mag release, just my not so humble opinion!