Not sure what the deal was with the memory. As the other live site just gave a 500 Internal Server error. But I do believe now, I know what caused it. I'm using a commercial theme and I think, one of the theme's settings along with a non-standard configuration setting in wp-config.php was causing it. I believe it was just a coincidence that your plugin was in the mix as you touched upon.
Going to resolve this for now. If I find anything else, I'll let you know.