This is a great plugin. I checked out, I think, every map plugin for WP and this is the best for what I need.
After installing the 2.38.5 beta I open marker and click icon to see available icons but there is no link for selecting custom icons. I created the wp-content/uploads/mappress/icons/ folder and uploaded some icons per your last message but no see so I reloaded the plugin to no avail.
I looked at readme.txt and your site and forum but could not find release notes.