When embedding a SWF file on a page or adding a YouTube video through the Widget macro the flash is scrambled when scrolling the page. Text and page elements from above it will display instead of the flash.

I could also reproduce the behaviour on the documentation page: https://confluence.atlassian.com/display/DOC/Embedding+Multimedia+Content

I extracted the code with the SWF and added the parameter "wmode=opaque" then the problem was gone.