Maybe you could just output your script in the footer, rather than the poi list?
The list is actually generated and then moved to its container <div> when the map is displayed, so your script tag is ending up inside a <div> – something I guess IE8 doesn’t like.
There’s also an action that gets called when a map is displayed: mappress_map_display($map). It gets passed the entire map in ($map). You might be able to output your script tags there as well.