While scrolling to see a long file name, the listed suggestion box selection disappeared in IE9+ (Ok in IE8).
RichFaces 3.x is facing AJAX rendering issues in IE9+: they won't fix it as they released RichFaces 4 for JSF2.
There is no satisfying solution for now, you can check:
We're currently using Richfaces 3.3.1.GA in the platform.
Note that in the RF4 showcase, the suggestion component has changed, see 2/lazyClient mode + autoFill attribute:
A workaround for the 5.7 release might be to simply remove the horizontal scrollbar, despite the length of labels. The main goal of the suggestion is to help user to identify the right document: as the user can see more than 100 characters, the help is still useful without a scrollbar even if the end of the title is hidden.