Descend now feature

Hi,

I was wondering if any one has the same experience as I. When ATC let's you down early;) , so before the calculated T/D, you must use DES NOW (when within the 50 NM limit from that point). The a/c starts a slow descent at 1000'/min. When the a/c intercepts the original computed descent path, the throttles ought to come back to idle (ARM), the aircraft should pitch over and intercept the path (and assume e.g. a 2200/min descend).
I've tried this several times but the CDU seems to stick to the initial 1000'/min down and doesn't alter this when the a/c catches up with the original VNAV path.

Regards,

JWS