Text editor not showing complete value

I have a 2 value in a row that is medium text, its looks something like this

but its not completed only first 259 characters, i checked throu phpmyadmin and the text is full and it looks like this:

<i><b>Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.</b><pre>\n</pre>Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.<pre>\n</pre>Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.<pre>\n</pre>Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.</i>

when i try to update a row its says :

When i delete the content of the first value , the second shows as full, when i delete the content of the second value the first shows as full.

Watch out for the UPDATE query in the SQL log after the error message. Please post it here (remove sensitive info if any).