VNAV Question

Hi all,I just bought PMDG 737NG both the -600/-700 and the -800/-900. I absolutely love it! I have a question about VNAV. When on a STAR, for example, VNAV sometimes "forgets" to keep descending. It seems to happen when there is a hard altitude to cross, followed by a waypoint without any restriction, followed by the next waypoint with a hard restriction. I can get VNAV to keep descending if I disengage, then reengage VNAV. What's interesting is the vertical deviation indicator will show I'm too high and to descend, but the aircraft will maintain the previous altitude.A flight example is:I flew from KPHX to KLAS and descended on the TYSSN1 Arrival. The plane crossed ZATES at FL190 and KADDY at 12000 & 250 without a problem. The next restriction is SUZSI at 10000 & 210. Between KADDY & SUZSI is waypoint TYSSN, so VNAV didn't keep descending to cross SUZSI at the restriction.Is there any way to make VNAV keep going?Thanks,Christian