Headliner Repair
No issues here so far and it's five years old.
2007 GTI base model, kept in Florida.
This fix should work for all models with falling headliners. My headliner lasted just over 3 years, and a VW OEM replacement (about $700 if VW won't cover it with their warranty) failed similarly. You don't have to go that route. If you try to glue the fabric back on, it will take black magic to have it look right, and it will fall down somewhere else even if you are successful.
SO - if you want a permanent fix, first, remove the headliner from the car. Then remove and discard the fabric. Thoroughly clean off the disintegrating, sticky foam with paint thinner or maybe charcoal lighter. Scrape at first, then wipe. This will take some time to do it right - It takes several applications of solvent to get the headliner clean. One extra cleaning is a good idea. From here you have a choice of putting some texture on the headliner, or simply painting it. That's your choice. You can even clean and paint it without removing it, but you had better carefully mask off the whole interior first. The sticky foam backing can get on everything and anything, is why.
When the headliner backing is thoroughly clean and tack free, you can a coat of apply thin epoxy resin thickened with talc (baby powder), with a paint roller, to the headliner. How much talc (or other thickener) to add is up to you, so experiment with a sample (on cardboard or similar) to get the texture and thickness to suit you, to look right. The approximate consistency is like very thick paint, or a paste similar in consistency to hand cream. The thicker it is, the more pronounced the stippling, and the more resin you will use. If you do this right it will look like a factory surface. I use a digital scale (eBay) to keep track of the test mix. If I had to guess, it's about one part talc to two parts resin. I will also mix resin and hardener by weight. You can use cheaper polyester resin, but you car may smell of styrene for months, and some people hate that smell. Just pay extra and use epoxy resin. I didn't use latex paint to texture the headliner, because if it comes off you will have another mess to fix.
When the resin sets, sand it to remove the highs so the surface isn't scratchy and rough to the touch, but sand lightly so the stippling remains. Epoxy resin and other accessory products are available from US Composites, on the web - quality products, reasonable prices. A pint kit should do it. Slow hardener, cooler temperature, gives more work time, which is desirable.
For a charcoal or gray interior, I suggest spray Rustoleum Automotive Bumper Paint (Home Depot, WalMart, or similar, about $8). It only comes in Charcoal. Bumper paint is tough. If you use regular spray paint you will find it is not durable. I used two or maybe three cans, multiple light coats. The Charcoal Rustoleum was a very close match with my Charcoal interior color. If your interior is black, Rustoleum makes a truck bed coating that is very durable (same sources, about $7).
This was a permanent solution for me. It looked OEM. When I sold the car two years later, it still looked good as new. The buyer felt it was an advantage not to have the problem recur, after he learned about the problem.
You should be able to find directions on this forum for removing the headliner. Know that wiring is fastened to the underside with tape. If you remove the wiring harnesses, mark or record where they go on the headliner back - before removing them. In fact, it would be a good idea to mark their locations anyway. An unsupported headliner is somewhat flimsy and not particularly durable, so take your time and be gentle with it. It barely comes out through the rear hatch when tilted, rear seats folded. Treat it carefully and gently. If you do bend it, you can probably repair it with a small piece of fiberglass cloth and the epoxy resin.
I hope VW has found a decent backing for this headliner. My 16 yr old Odyssey's headliner is still intact and stuck on tight. Just bought a 2017 GTI, so we will see. There was no reason for this to happen on my 2007, and certainly no reason ten years later.