If anyone doesn't believe me, load a mag and leave it the fully loaded state for a couple of months, then compare it to one that you'd fully loaded last week. There is a measurable difference in pressure. Is that pressure enough to make your pistol malfunction?
I have a Colt Delta Elite, first run as opposed to the more recent second run, with original Colt mags and some Wilson Combat mags. I have had to replace the mag springs more than once over the years.
Running 10mm auto in a 1911 is pushing it a bit more than .45 auto. Pressure and slide velocity increases with the 10mm. When the mags have been left loaded for long periods of time, and/or used quite a bit I start experiencing failure to feed/FTFs. Immediately after replacing the mag springs, FTFs are gone. (It is also interesting to note that the WC mags allow for one additional round over the Colt mags.)
I am currently waiting for some new ISMI springs to try out in my Wilson Combat mags. The original Colt mags are running Wolff +10% and at the moment are running fine.
So, yes leaving mags loaded to capacity for long periods of time can adversely effect the mag springs; at least in this particular instance. I have left a couple of original spring WC mags loaded for a couple of years since about new and they were problematic/FTFs after sitting for that long. (I was curious to see what would happen and had the extra mags.)
I do think that application is important in this issue. Springs can be pushed to the edge, or over it, of the physical limits of the materials/manufacturing process and the design of the magazine and the gun.
My Delta Elite seems to be very sensitive to the relative magazine spring strength. Also to the addition of an extra round; in the case of the WC mags. Seems that I have heard similar comments made about 8 round versus 7 round 1911 mags in the past, in the traditionally chambered 1911.