Paypal Button Codes Deteriorating

[CloudForest]

Hi!
I've used the Education theme for one client, and I'm about to build another client's website on this theme, but both of them are giving me trouble with Paypal button codes that are deteriorating over time.
See http://www.patrickecraig.com/store/ - his Paypal variations dropdown has changed several times to being two separate items, and I think it was the button Paypal button that has stopped linking to Paypal before (it is currently).

I'm not sure if it just happens by itself over time, or if you have to be on the page in the Visual editor for it to happen, rather than the HTML editor. Either way, it's not ideal for most clients who don't know how to fix the deteriorated HTML code :)

Can you fix this?
Thanks!
~Leah