I didn't look into those yet but I think they are caused by a bounce on the ramp. I am not certain, though.
A good way to test this is to make a map that reliable makes the player bounce when hitting a slope using the bounce table.
One could also patch the bounce code back into ioquake3's baseq3 and print a message once the bug occurs.
If this effect is caused by a bounce, I don't see a way to fix it. One could write code that removes bouncing from ramps but there are a number of maps where bouncing on a ramp actually is used to speed up in a 100% reliable way.
Hm... one may fix this by only banning bounces when the player still has positive Z-Velocity and hits a ramp. That would fix the 'lowjump' issue.
The not gaining speed problem is probably not fixable unless you have some kind of convenience check like a "Only bounce if player does not hold the jump button" kind of test when hitting a slope.
However, this is a defrag issue. We(mDd) can't do anything about it. I guess mappers just have to use the noob surface parameter and hope defrag 1.92 will become stable soon.
Patching playermove code is not easy serverside if possible at all. We won't do it.
Cgg is the only one who can fix this.