WordPress Closes Tags and Breaks Dropdown Menu

I’m trying to use a Paypal donation form. When I first put it in, it works, but when I update the page after that, it breaks. From what I can tell, it’s adding extra <select> tags when it shouldn’t.

I paste this:

<td><select name="os0"><option value="Option 1">$50.00 USD</option>
<option value="Option 2">$100.00 USD</option>
<option value="Option 3">$500.00 USD</option>
<option value="Option 4">$1,000.00 USD</option></select></td>

But when I save it and click on the Visual view and then go back to Text view, it changes the code to:

<td><select name="os0"><option value="Option 1">$50.00 USD</option></select>
<select name="os0"><option value="Option 2">$100.00 USD</option></select>
<select name="os0"><option value="Option 3">$500.00 USD</option></select>
<select name="os0"><option value="Option 4">$1,000.00 USD</option></select></td>

Which breaks everything.

Is this a known issue?

[Moderator Note: Please post code & markup between backticks or use the code button. Your posted code may now have been permanently damaged by the forum’s parser.]