You need to define your parting line to be offset from the rounded edge rather than using the round tangent to determine it. On the left side of your image, the parting line was the edge that existed before the round. Once rounded, the parting line now has to be at the tangent of the round. Redefine your draft so that it is offset from the edge and the round then will be entirely on one side of the mold.
I've sketched over your image a crude approximation of what I mean.
Adding the round is changing the draft split. When sharp, the split is at the sharp edge:
Adding the round moves the split down slightly, to the tangent of the radius (a bit hard to illustrate):
Allowing the radius to define the split might also create an uneven parting line.
I'm not suggesting that the height of the straight parting line be changed, only that you define the parting line around the front away from the edge that you want top round:
This will give you a nice, smooth edge to round and will provide your tool maker a nice cleanly defined parting line to build the tool to.
