Right Right!! I see that every now and then. I see "exciting" and "interesting" more often.
Yea, "I am disappointing in you" should be "I am disappointed in you."
I guess there is confusion with those words because they are in the present tense form and people think using these words in the present tense form describing somthing happening now would be correct when it is actually not. One of the tricks of English grammar that can be hard to explain.
That's why it is important for people to read, read, read, and read! 
