3.9.1 and PayPal button drop down list

This has always worked for me until now.

I post a button with a drop down list into the text view. It looks like this:
<select name=”os0″>
<option value=”Full Registraton”>Full Registraton $499.99 USD</option>
<option value=”early Bird (exp Aug. 31)”>early Bird (exp Aug. 31) $399.99 USD</option>
<option value=”Deposit Only (bal due Oct.1/14)”>Deposit Only (bal due Oct.1/14) $200.00 USD</option>
</select>

Notice the select tag has three option values. If I open a preview window the code works perfectly. But if I return to the editor and switch to visual mode, WP re-rites the code to this:

<td><select name=”os0″><option value=”Full Registraton”>Full Registraton $499.99 USD</option></select>
<select name=”os0″><option value=”early Bird (exp Aug. 31)”>early Bird (exp Aug. 31) $399.99 USD</option></select>

Notice how it inserted new select tag for each option value.

How can I stop this behavior?

Any help appreciated.

Kerry