Thank your for your tip and your very fast response!
Hover tips are not shown on my hosted server and my own localhost too. All the external Q2A sites (perhaps 10), where i have visited, are not showing hover tips, except this Q2A home page!
Solution on scratch:
In qa-mouseover-layer.php is on line 56 $text allways empty. So i read the content with extra code. Its not fine, but functionally for the next hours.
I love Q2A!