obviously its not resolved. the strange is, that this do not occurs every time.
I solved this with the trick, that I changed the superclass of the labels into webtextfield with a non-bordered Style. The appearance is the same and it works.
It has to do with the level of embedding. WebLabels which are nested inside multiple levels of WebContainers suffer the most from this bug, while ones in a single level hardly show the problem at all. Fixing this bug is a whole other matter.