Do babies lose some skills as they are learning others?

My little boy (10 months) just in the last few days learned to clap on his own. When we clapped or said the word "clap" he would do it. But now he doesn't do "kissie" anymore when we tell him to. Then last night we discovered he knew the name of one of his toys so we were practicing having him pick it out of a "line up". Now today he won't do the clapping. Is this unusual?