Not sure if this is typical but does anyone else notice their short 10 round factory mags supplied with their new Glock holds 11 rounds in the mag? Of course when I stuff that 11th round in it seems like the spring is near totally compressed, but its not difficult to squeeze it in. Naturally I dont carry it with 11 in the mag as I"m concerned the spring will grow weak quicker, but I found it interesting in that configuration I have 12 shots including one in the chamber all the while it fits neatly in my front pocket

It is typical.  I can cram 18 rnds into many of the G17 17-rnd mags I own.

I advise against it, however...I believe it could "over-compress" the spring.  Don't load 'em beyond their listed capacity.

Hell, I've got some 17-rnders w/factory +2 extensions on them I've accidentally crammed 20 rounds into.  Fuck that.

Don't load over listed capacity, just to be sure.

I've done it on accident when reloading my carry ammo after a day at the range, I was looking all over for that 10th round for my second mag.  I finally re-unloaded the first mag and found that missing round.

I agree with Vin, leave it at 10 unless you add an extension.  I'm more worried about the spring binding if it's that compressed, and that wouldn't be a good thing for a carry weapon.