“Read more” insertion point not working

So I’m working on this clients page and he’s got something like 45 post on the blog page.

In the admin area under All Post its showing like 5 pages of post. Each of these post is a book review and rather verbose. So I’m having to go through all of these post and insert a “Read More” link a couple of paragraphs down. OK so fine I’m down to about the last 14 post and all of a sudden the “Read More” link insist on inserting at the end of the post instead of where I click ( setting the caret) in the body of the content. It has just started doing this after 30 something post. What has happened to make WP start malfunctioning? Is there a fix for this. The first time it did this it had inserted 3 of them at the end of the post (off screen) before I discovered what was happening. so after deleting all of those and trying again it does it again, and again after repeating this process 3 or 4 times it finally worked correctly. This last time I’m on about my 10th failed attempt. I’m about to abandon the problem and just advise the client that it’s an issue with WordPress. Fortunately it’s 30 something post in so maybe he will be willing to overlook it.

I can only hope someone here can advise me of a fix for this problem. BTW I’m using the tools at the top of visual editor.

The page I need help with: [log in to see the link]