I’m sorry I’m coming to this a little late, but perhaps this will help you understand the logic of the idiom a little more:
It is no trouble at all.
It is not any trouble at all.
Indeed, that helps somewhat – thank you, Bev.
(Actually, we too have an equally illogical expression used as a reply to “thank you”. You are most likely familiar with the French “De rien” literally meaning “Of nothing”. Similarly, the Romanian response “Pentru nimic” literally translates as “For nothing” – so there! :-))
Even nuttier!
Makes you think of the ironic “Thank you for nothing!”, doesn’t it?
Quite needless to say, I never use our “Pentru nimic” either! While I’m at it: I suppose the Romanian reply “For nothing” is meant as “There is nothing (you need) to thank me for”.