Thanks for your replies.
The penalty to melee is described as "an additional -40 OB modification", so that is tacked onto the -20 for not having full % activity to devote to your melee attack.
The question is: How many percent CAN you devote to your melee attack? The rules simply say that if the cancelled action is at least 60%, you can make a melee attack. It does not say that you can "make a melee attack with the percentage of the cancelled action(s)". I DO agree that this makes sense somehow, though.
Nor can you make a full melee attack for the +10 bonus. "the target of the attack must be declared during the Action Declaration Phase". (RMSR, p. 97)
Since there are only three types of melee attacks (there is no "normal melee" - just full elee, press and melee and react and melee), you MUST chose one of those. And I'd NEVER allow a "react and melee" after a cancel action. Also, press and melee calls for at least 60% activity, whereas you can cancel a 60% activity and melee, so that one's out, too. I see it as you get a new declaration phase immediately when you cancel action, where you have to declere movement, maneouver or melee - and if you choose melee, you HAVE to choose full melee, and state your target then and there.
As for the question: What if I have used 20%, cancel action and choose movement - then what? The rules say I get 50% movement, it does NOT say that this is reduced based on the previous activity. Thoughts? I think this should be seen together with the melee option.
And what if I were hasted, had to cancel 120% activity and attack in deliberate? I say I STILL get the -40 penalty. And still only one action.