Generally speaking, it so appears ... as you said, "...speed increases, the nose pitches up..."

Actually, the plane may climb a little, but at the same trimmed wing AOA into the relative wind.  

I learned to climb a little higher than cruise altitude,  then set power for cruise, and then descend back to cruise altitude and the plane increases in speed from the altitude energy and holds the increased cruise speed at cruise altitude.

I never thought of the laminar flow gradually attaching.... and the trim remained steady, I think.  We had the trim on the yoke between the right hand thumb and forefinger. : ) so maybe it did vary.

Seems like if the laminar comes and goes as you say, one either has to chase either altitude or speed.  But I believe the wing's AOA is trimmed by the tail.... regardless of altitude or speed.

imho

Your plane is very clean.  Maybe it's getting hit with sticky air molcules than hang on and then slip off?  

: )

 power changes or