[Membership 2 Pro] More tag content showing in source code

I'm using the Membership 2 Pro plugin to manage our subscription and we use the more tag to protect the content but it's come to light that the content is still available in the source code making it very easy for people to find the full content.

Is this normal behaviour for the plugin or could our theme be doing this? I need to find a way to ensure that the content is not visible in the source code.