I implemented a workaround in MapPress 2.41+, but I’m not sure it works in all cases. Please provide a URL.
For the outer scrollbars, here’s some things to try:
1. Install the latest MapPress
2. Use a bigger (taller) map
3. In the infowindow CSS, give Google a hint that you want the infowindow wider, for example ‘min-width:500px’
4. Use the MapPress ‘infobox’ style instead of the standard infowindows (the infobox sizes correctly).
Google only applies the outer scrollbars. The inner scrollbars may be coming from the infowindow content. Is the CSS ‘overflow:auto’ applied somewhere in the content of the infoWindow? You can use Firebug or Chrome/IE Developer Tools to check.
The double scroll bars went away, though the single scrollbar was persistent. I tracked that down to some CSS edits. Looks pretty good now. The only bummers is on a mobile device where the map pins in the links below the map, and the text links go wonky.