Basically my rationale is that Centova Cast works fine in all browsers without this extension installed. The LastPass extension modifies the HTML/JavaScript code (via DOM manipulation) generated by Centova Cast to inject its functionality into the page, and in doing so, it's breaking Centova Cast's HTML/JavaScript. Therefore, I consider it to be fairly clearly an issue with the LastPass extension... no extension should ever break a web page if it's designed correctly.
Does this extension have an option to blacklist certain domains (eg: to exclude it from use on certain sites)? If so, I'd recommend using that. If not, we may have to find an alternate solution, although I'm not terribly keen on diverting development resources into workarounds for problems that arguably aren't ours in the first place.