Assigning modwheel to osc pitch = very uneven pitch change?

[Barnelby]

Let me elaborate-

When I assign the modwheel to control osc 1 or 2 pitch (or both) and draw a line of automation, the pitch does not adjust smoothly... rather it goes up or down in "bumps" and sounds like an engine slowly revving... anyone ever dealt with this? I can upload an example if needed.