Thanks Oliver, Charlie (here too), Chris and Steve!
Despite the gloss coat and extensive use of setting solution I got some "silvering" due to air bubbles underneath some decals. Fortunately for me the slivering somehow blended with the weathering, so it doesn't pop to the eye too much.
Since I adopted the "standard procedure" successfully on many other models, I put the blame on the "quality" of the decals, that matches the overall quality of the model.
Indeed, as you say, Steve, the dull coat brought it all together. I was astonished about the effect myself.