[my_controls]

Hm interesting, I just don't see our aircraft doing that though. If I use cruise descent to descend prior to my T/D then as I get closer to the original path, the path that was computed back when I was level, the plane will pitch down and reduce power to idle and capture the path.

As stated in the manual regarding early descent:

"A descent in VNAV started before the top of descent point is an early descent. If a path descent is planned, VNAV commands a 1000 fpm descent until the idle descent path is intercepted."

The way I interpret your post you're saying that the plane will cruise descent down to the altitude in the MCP window at 1000 fpm, and that it won't have any path information until it reaches this altitude. Is this a correct interpretation?

I did however find another segment in the manual about a special program called energy compensation which may be what I was seeing before.

"The FMC uses a special program called energy compensation at certain times during an ACT PATH DES. This program goes into effect when the MCP has been temporarily set to an altitude above the planned descent path. The airspeed cursor will slowly move toward a slower airspeed while the "TARGET" speed on the FMC remains constant. The airspeed reduction improves the capability of recapturing the descent path. When the airplane is cleared to resume the descent, the airspeed will slowly build up to the FMC target speed as the airplane recaptures the planned descent path."

I have seen that happen before, usually when you pass the T/D point without descending. The plane starts slowing down towards the min clean speed. I don't think this is what's happening though but I could be wrong.

On a side note I still don't fully understand the difference betweet a FMC SPD descent and normal lvl change either.