Round Corner rectangle inside bleed

Late reply here, but I just had the same problem - glad I'm not the only one! I decided to modify the design in the end because it's not a deal breaker. A real conundrum.

You have have set an impossible task for yourself. Bleed exists because the cuts are not going to be 100% precise, and therre is no smooth way to continue the color into the bleed with your current design. 

If you put your rounded corner exactly on the edge, it will look wrong every time the die moves even a little; either a sliver of white or the top of the curve cut off.  

I think that a better solution would be to move the curve a bit in from the edge top and bottom. That will ensure that your curve shows as intended, and looks consistent on all pages.