Problem with Google Maps plugin when inserting maps in posts

I’ve noticed a strange behaviour with Google Maps plugin, version 2.8.1. In one multisite installation (blogs are located in directories, not in subdomains), the superadmin can create maps in post and pages, but other blogs admins only can create maps in pages, not in posts.

When these users edit a post and click the Google Maps icon, the popup windows appear blank. On the other hand, when they edit a page, the popup window works fine.

I think this problem has something to do with paths, post types or subdirectory installations. When I click the Google Map icon in one of the blogs of my multisite installation, I open this link, which doesn’t work:

But when I click in this link, it works fine:

Notice that the second URL includes a post type segment.

Any idea? Thanks in advance.