run attached example... in IE8 (can be reproduced in IE9/10 with document mode IE8)
1. scroll down in div...
2. hover one of the labels
3. tootip appears (after server event)
4. scrollposition of div is reset to top (only happens in IE8)
if the vflex is replaced by height="100%" the problem does not occur -> so it is probably "vflex" related