Thrust/Speed goes down to minimum in CRZ Mode

Hi guys,

when I was climbed to CRZ Level (in VNAV) the speed goes down until minimum speed (then the 777 pitches nose down to get more speed). 

The N1:

CLB: 99.3

CRZ: 84.3

What is the reason of this? Why can I fit it? I do not like to fly the whole flight with SPD, LNAV and ALT..

Thx a lot!

Edit: I don´t use Active Sky. I use the freeware FSRealWX v1.06