Following the forum advice I tried to fix the Velcro problem by glueing with sikaflex 291, but unfortunately the result was rather double disappointing: the pockets came off even faster and moreover the sikaflex remained on the hull having attached to it a part of the Velcro glue layer
Obviously the Velcro glue not only liquefies on warmer days but also has a higher affinity for Sikaflex than for the Velcro backing layer.
Now I removed all sikaflex from the hull again which is a serious job for a rainy or stormy day. Then I tried to peel off the glue layer from the Velcro as suggested. After five hours I really admired Simon's efforts since my peeling speed was approximately 2 inch per hour only. Fortunately my wife discovered meanwhile a fabrics website offering Velcro lookalikes without having a glue layer attached. So finally I replaced the soft band of the original Velcro for the new material and glued everything with Sikaflex 291. I am quite confident that this should work out (if not I will let you know).
Looking forward to pretty sailing without flying pockets,
Black Sheep
CC104