"don't know what the problem is..."
I've had these bags for years and never had a problem - 1 of the spare duvets has been inside it's bag for probably about 2 years now and still flat as a pancake. Don't have any trouble sealing it - the zip works fine. Just coming back to re-order some more. You can fit heaps inside them and they really free up space. Bear in mind the compressed weight of clothes/blankets etc seems more than when in their normal state so a full bag can be quite heavy!