Apologies if this has been covered already...
 
   I find that when I'm editing controllers in the piano roll, using the smart tool, that I'm not able to draw single data points for a CC. I can draw lines, but if I try to draw a single data point using freehand mode above or below existing data, nothing happens. I would believe this is on purpose except that it's giving me a pencil icon, yet won't write data. It seems like either a minor UI bug (I shouldn't get a pencil) or a functionality bug (it should draw when I click!).
 
To Repro:
1. Using the draw tool, put in a couple of CC values - being sure that those values are far apart (so you're getting a big long line between them)
2. Put your smart tool either above or below that line, and you'll get a pencil icon, but you can't actually draw.
 
I should note that switching to the regular draw tool works as expected - I can draw as many little neurotic CC controller points as I like. On a side note though, it does seem the 'dead zone' around the existing data is a tad wide. I have to zoom in quite a bit to be able to specify to within 2 or 3.
 
Thanks for considering!
Mike
Sonar Plat Cambridge
Win 7x64

Hold down the Alt key when using the Smart Tool to insert individual CC events.
 
Hope this helps,
Ron

Another factor: clicking in the time line, or doing one of a number of other things, can result in unintentionally Selecting one or more notes.  And then, you can't draw in the controller lane for notes other than the selected notes.    I am constantly battling this.   My workaround, since with the "smart (stupid) tool" you can not make a note with a single click: click somewhere NOT on a note in the PRV, that unselects everything.   Then you can draw in the controller pane as you might expect, creating a curve for whatever controller you are using. 

williamcopper
Another factor: clicking in the time line, or doing one of a number of other things, can result in unintentionally Selecting one or more notes.  And then, you can't draw in the controller lane for notes other than the selected notes.    I am constantly battling this.

 
It's not having notes selected that prevents you from editing controllers on another track, it's that selecting a note moves focus to that track, and obviously you can only draw controllers on the active/focused track. Deselecting the notes won't move focus to a different track that you want to edit. You would still need to select that track in the tracks pane or select a note in the PRV that belongs to that track. Controller lanes are differentiated by type and channel only, they don't belong to a specific track.
 

brundlefly
It's not having notes selected that prevents you from editing controllers on another track, it's that selecting a note moves focus to that track, and obviously you can only draw controllers on the active/focused track. Deselecting the notes won't move focus to a different track that you want to edit. You would still need to select that track in the tracks pane or select a note in the PRV that belongs to that track. Controller lanes are differentiated by type and channel only, they don't belong to a specific track.

You know, that might be one of the most straightforward, succinct descriptions I've seen for how CC lanes are set up in a multi-track PRV.   Particularly that last line.

Thanks, Steve. Yeah, I think that last part is not intuitively obvious and catches people out, especially as it relates to the debate around the fact that Bounce to Clips writes the forced MIDI channel to all events in the clip.
 
Having event channels match forced MIDI channels can make it seem like each track has its own dedicated controller lane. In fact I often deliberately use that "feature" to re-write event channels so I can treat controller lanes as dedicated.
 
But, as has been pointed out, if you do a lot of  copying and pasting events between tracks and then bouncing some to clips and not others, there's potential for a lot of confusion about which controllers go with which tracks.

Nicely said (three posts back), brundefly, but wrong.  Or, rather, not relevant.    Re-read my post to which you gave a misdirection.   The rest of what you said was ok, but specifically: if you have only ONE track involved, you still will lock up the controller pane by having one note selected.   That is, you cannot draw to adjust note velocity: the controller pane, the Note Velocity line, cannot be adjusted by drawing on unselected notes.   
 
This might be desirable in some cases, but as I said, getting notes selected accidentally by clicking in a slightly wrong point happens constantly. 
 
I fervently want CW to fix the controller pane.     Maybe I'll make a video of me fiddling with the controllers, starting with a hash of 90 thin lines and having to delete them one by one in order to be able to get to the one I want.    While the screen jumps with each change, so the mouse needs to be repositioned each time.      

Oh, and the OP mentioned the "dead zone" ... that too is a big problem.   Once again, CW deciding to make mouse clicks fit within a tiny tiny area.     You can not make a new controller differ from the previous setting by a little bit, since the mouse 'snaps' to the previous controller value.   Another big time waster:  you have to draw a big change and then modify it to a small change.           And did I mention that all the controllers have the same size?  so to get to one, in detail, requires using the entire screen because all the others want to be just as big.     Please work on this ....

And one more thing: this was posted by the OP as a problem report, which it is.    But yet again someone locked and moved.     Why why why do you need to do that?    I'm sure who-ever is responsible for reviewing the problem reports is capable of skipping those that do not seem of current interest, while everyone who has the same problem as the OP has to follow a link, leaving where they had been in forum-reading. 
 

To support the OP, further: the visual feedback mentioned (you see a "pencil" so you expect to draw) is a valid issue, bug, or feature request: don't fool us with the visual feedback.  If it can't be done, don't show it as possible.