Hello,
Seems like you are confusing the two applications. MDG uses different BRF+ applications for different purposes. You are talking about two different applications that are not directly related: one for the workflow routing (rule-based workflow), and one for derivation and validation.
The derivation and validation BRF+ application is run interactively. At step 00, which is your first step when the user is on the MDG screen, that BRF+ application will of course work; NOT because it is step 00, but because a user is actually editing the request.
First suggestion, do not try to force the two to work together. They were designed for different purposes. Please understand how the two applications work before getting yourself in deeper trouble.
Second suggestion, please learn more about BRF+. BRF+ is a generic application that can be used pretty much for anything. It is not specific to workflow nor to MDG.