Why adding "Scale Velocity" removes Gravity?

I’ve particles spawning with a burst with “Velocity from point” and gravity and it works as expected. They burst in all directions and fall with the force from the gravity.
Then, I add a Scale Velocity with the default 1.0, 1.0, 1.0 and I don’t know why, the gravity stops affecting the particles. Shouldn’t a scale of 1.0 do nothing?

Something like this:

If I disable scale velocity the gravity takes effect again.
What’s happening here?

I don’t need this anymore. I’ve solved my problem in a much better way by using the “Drag” module.