Remove it and solve the problems natiely it does solve for you.
RocketLoader does restructure and re-arrange your files in the DOM if they are not arranged perfectly. So if RocketLoader does block rendering the page for a long time this means there is much to do, much to improve.
Just test how your page performs with RocketLoader and how without.
If it does perform better with then dont care about the renderblocking as without your site would be even slower.
Best way is to natively optimize your site so RocketLoader can not optimize it even further and then remove RocketLoader.
Am i right that you are using WordPress?
There is nothing to fix, this is how RocketLoader works. It blocks rendering, optimizes your DOM and when finished optimizing it, it does not block rendering anymore. So there is nothing to fix from CloudFlares site but from your site - optimize your Site/Application to do better natively.
Native optimization is alway the best, most powerful and the one that you can kepp independent from what additional services you are using.