Pages 5.2 won't create new style

I've suddenly hit a bug in Pages 5.2. It just won't create a new style.

I've been doing the following:

1) Highlight the text I want to create the style from

2) Click the plus button on the Paragraph Styles list

Before this brought up a text field into which I typed the name of the Style. In this case 'Title'.

Now what happens is that all the styles disappear, and although a text field appears it won't allow me to type anything into it.

When I return to the document I discover that the Style has been created but it has the name. 'Fre Te Form 1'.

I tried renaming the style by clicking on the arrow to the right of the name and selecting Rename Style. This time I was able to enter the new text Title but when I hit return to enter the text it just reverted to Fre Te Form 1. Has anyone any idea what I should do as this is driving me to distraction.