I'm automating the send level on a track. While I hear the automation working (it's the send to a reverb bus), the level knob for that send doesn't change with the automation. Is this a bug? 

It should work sharke - it does here.
 
Have you tried shutting Sonar down & re-starting?

Sharke, your not the right person to mention offset mode to, but... ?

Nope restarting doesn't help...not in offset mode, no....the damn knob just won't turn!

If there's more than one send on the track, make sure you have the right one showing in the Inspector/Console.

Reassign the envelope to something else and see if it controls that?

I don't know if this is related, but when automation didn't work for me, I needed to enable the track's "Read".

Don't think I've explained the problem clearly - the automation is working (from an audio point of view), it's just not turning the send knob (from a visual point of view). It's definitely the right knob, it's the only send on the track. 

another skylight redraw bug?

I`ve had problems with this too that could be solved with offset settings. See this thread: 
But there are still some issues regarding automation not showing in controls (mentioned in that thread also) that I assume are bugs, unless they can be explained by someone. They disappeared spontanuously though and things seem to work fine for me now.
Does automation by chance show when the write button is enabled?