The solution requires us to make some fairly significant changes under the hood which will need to be well-tested before they can be released. So I made the decision that we would go ahead and ship R5 so that you can start developing and testing your apps. We will ship an update (5.1) that will include this fix once it has been well tested. These updates will always work with any license key that worked with the major release (R5 in this case) so you don't need to worry about missing the fix.
This issue ONLY affects deployment as FastCGI. It does NOT affect building your app as a standalone HTTP Server.
We apologize in advance for this last minute issue. We will get you the update as soon as we can.