Cam,
A good rule of thumb is that you should never store your magazines loaded to capacity. Some will tell you this is bunk, but I have witnessed the spring-memory issue on multiple firearms from multiple manufacturers. It's best to store them with 1-3 rounds short of full capacity, carrying will be your exception obviously.
I always buy extra magazines and I have exercised the habit of rotating those magazines out once a week. This helps relax those mag springs so they aren't constantly wanting to release that stored up energy from being loaded. Since magazines don't compress in a uniform fashion, it's easy for the springs to develop weak points. I don't have an answer as to why in the physics, but it happens.
My military issue Beretta 92FS mags, brand new when we got them, lasted about 2 weeks fully loaded then went to crap immediately. The Italian magazines for the same pistol worked flawlessly for 10 months rotating on a 2-week basis. I've had Glock 30 magazine springs go bad without a reason as to why, Glock took care of me. The same goes for my M-16/AR mags, I rotated the loaded ones out weekly when I worked with them.
CZ magazines, same issue after 2 weeks without rotation. Para Ordnance LDA mags, same issue after just 3 days. Sig Sauer mags, same issue but those took 6 weeks fully loaded stored in one heck of a humid location (not mine either). Ruger 22 magazines have been the worst for me, don't store those loaded at all due to their unpredictability on spring-memory; some will have no issues and some will fail within just a few days, it's boggled me for a while that we had this happen on brand new mags.