Hi mdcooper, I'm inclined to agree with you. Many of my Italian friends agree with me, others don't. Langauges evolve and usage changes. When I first encountered Italian I heard Lei used a lot more than it is now. I suppose it comes down to a matter of personal style or standards. I hear many native English speakers tell me that they "Seen something interesting" and quite a few 'Have done good' when I'm thinking that they have done well. Personally, I'm no King Canute, I won't even attempt to keep the tide back but I do try to find the nice higher and drier ground to keep my own little toesies nice and comfortable.
Well, I found a way to get it wrong. ;-) I put "I am busy" because I thought "I am full" would not be used in Italian. (I've studied French and that would not be polite to say so I thought the same would be true for Italian.) Anyway, busy was on the drop down definition list but not accepted. So, it is possible to get it wrong even when that seems impossible based on the clues provided....
It seems when "pieno/piena" are translated as "busy", it's used more with places or time periods: "una settimana pieno" = a busy week; "È sempre così pieno nei fine settimana?" = Are you always this busy on the weekends?"
http://context.reverso.net/translation/english-italian/busy#pieno gives examples of "pieno" translated as "busy".