Loses Teaser on first save, when imagefield also present

I have a page containing (only) the standard Title field, an Imagefield (version 6.x-3.2), and the standard Body field using FCKEditor.
When creating a new page, enter Title, upload a new image to the Imagefield, and put into the Body:

<p>teaser</p>
<!--break-->                                        (This is a teaser break, but does not seem to show in the preview)
<p>body</p>

On the first Save operation the Teaser is not saved, though the body part is.
The same happens if one uses Preview rather than Save on the first entry.

If the teaser is then added in another edit operation, it works correctly.
If the imagefield is left empty the first save works correctly.
If the image field is uploaded, the page saved, then the teaser and body added in a second edit operation, it works correctly.
If FCKEditor is switched off, and the plain text editor used instead, it works correctly.

Regards, Tony.