fix for #282

This issue is caused by the inproperly triggered 'mouseenter' event when scrolling happens.
To fix this issue, we need to capture the event and prevent it from propagating if it is triggered by a scroll (which is handled by the _ensureHighlightVisible function call ).
Due to the fact that mouseenter event is triggered differently than normal dom events that bubbles, see: https://developer.mozilla.org/en-US/docs/Web/Events/mouseenter, changing ng-mouseenter to ng-mouseover would enable as to capture the mouseover event and prevent it from propagating.