Long Magazines in Compact Pistols

I used to use 15 round S&W Model 59 magazines for spares for my 6906 which takes a shorter 12 round magazine. I never had a problem but quit using the mags for the 6906 when I read that S&W said the practice could result in jamming.
 
 I have a couple of long Glock 9mm mags and find that I get at least one jam per mag (30 rounds). The mag was made by Scherer. The jam is when a round doesn't chamber.
 
 The same gun with 10-rounds mags never misses a beat.
 
 Does anyone have an idea of the cause and a cure?

I think it has to do with the fact that, due to there not being anything on the bottom to prevent it from going in further than appropriate, it can place the cartridges too high for a proper feed. The mags designed as extended mags have a stop (where the bottom of the mag well is) to prevent the mag from going too high. The 15 rounder is not designed for the 13 round gun, so doesn't have this catch, or rather it doesn't have it in the right place for that gun.

That must be it. I've got a couple of Wilson Combat 8 round 1911 mags for the Officers Model and the floor plate of the mag goes up the front of the mag body about 1/2". Probably to prevent the magazine from being inserted too far.
 
 Thanks,

There is one exception that proves the rule.
 
 I have a Sig 245 .45ACP that comes with 6-round mags.
 Sig says they manufactured the 245 to use Sig 220 .45ACP magazines. The must hold closer tolerances or something like that to make 'em work properly.