Technique for self-adhesive puncture repair patches Is there any special technique for using self-adhesive puncture repair patches?

Today, I've had two different tubes fail within a minute of being inflated because the air pressure had split through the glue, effectively forming a little pipe from the puncture out to the edge of the patch. These were both patches that had been on the tube between one and three months, and I've had other patches fail the same way.

I figure I've not done anything catastrophically stupid, since the patches haven't been failing immediately. I've followed the instructions on the patches as closely as possible ("Lightly scuff tube with sandpaper. Peel backing from patch and press patch firmly onto tube. Tube must be clean and dry for patch to adhere." &ndash; that's it). They're decent quality patches (Park Tool GP-2).

I've never had any problems with old-school glue and patches. Is there something I'm missing or are pre-glued patches just useless pieces of excrement?
This kind of failure is basically the reason sticker-type patches have a reputation for not being reliable. 

Scrupulously sanding the area and getting it as clean as possible (ie, with alcohol or other residue-free solvent, cleaner than anyone can probably get it on the side of the road) wards off the problem but doesn't eliminate it. 

Sticker type patches are essentially bad products. You can't trust the tube long-term, so you really should change it back out when you get home, because if you don't you'll likely get another flat sooner or later when it fails.

Vulcanizing patches are superior. The system of carrying a spare tube and a vulcanizing patch kit, using the patch kit only if you get multiple flats in the same ride (should be a very rare occurrence), and patching your punctured tube when you get home so it can become your spare is popular and time-honored because it works and is cheap. You almost never actually wind up using the vulcanizing kit on the side of the road, and when you do it's no big deal because you've developed good technique. Vulcanizing patches make the tube as reliable as new, so it's fine to leave the tube in there and forget about it.

Self-adhesive patches play to peoples' desire for a simple one-step solution, contrasted to how vulcanizing patches do require a degree of technique and care - keeping track of where the puncture is, applying a nice even patch of glue that's the right size and waiting long enough for the it to dry, comprehending at all that you let the glue dry and then apply the patch, handling things carefully so as not to contaminate the patch contact surface or the tube with skin oils, etc. A lot of people running around now just can't and won't jump through those hoops, and in that sense there is a place for self-adhesive patches, but what's unequivocally true about them is they don't save time or hassle once the need to change the tube out again later is factored in.