large insert to edit area overwrites next field and corrupts list of editable fields

Hi,
background: each page on this site has 2 fields that the client can update.
I've just handed over the site to a client to "practise" updating the site - the first thing they did was cut and paste their multi-page cv into the first field and saved it - the result was the page engulfed the second field, the contents of the second field is now attached to the end of the first field and where the second field should be is empty. at the same time when you go back into admin and look at the pages to edit ,all pages and fields AFTER this corrupt page are missing. if I delete this page the database corrects itself, but if I cut and paste a multipage document into a field is truncates and means to destroy the other fields on that page as well as making the other pages after this field unreachable.
its seems to be a limit on the size of the text, (my client would like their Cv on a scrolling page)
are there any error checks to stop data over writing other fields?
see - biography.php the bad one - this is what is used to look like with a small amount of text: background.php
thanks
(I have raised this in support)