I just published a post with several Google Maps embedded in the post. I needed to edit the post several times (see my other question) and every time I edited the page the code for the embedded maps turned into “read more” links. Not sure what was happening but I ended up having to reinsert the embed code every time I’ve needed to edit.
Are you using Markdown mode? If not, that may be the issue. Also, note that javascript won’t stick inside posts. That could also be the issue.