I am using Processing 1.0.9 and am trying to reduce unnecessary CPU load by
calling noLoop() and then drawing frames as required using redraw().
Although this generally works, I have a problem with some animations where
a state is updated during the draw() processing: I know that a new frame is
required but redraw() doesn't work from within the draw() method.

The reason for this is that in the PApplet.handleDraw() method the redraw
flag is called after draw() is called. If this line is moved to the start
of the enclosing block then redraw() works the same wherever it is called from.

It's *possible* to work around this in your own code, but this would be a
lot easier if this was fixed.

If you need help to implement this let me know, but it's really a trivial
change.

not entirely trivial, because this can get stuck in a recursive mess, but
i'll make a note of it to see if there's a way to handle the situation.