I am running 21.2b13 on NT4.0, but do not know one way or another whether this is a new problem or a platform problem. A numeric or c-U argument to c-X ) repeats after defining properly, but the keystrokes that make up the argument itself become part of the macro definition. They are left in place after executing the macro and so affect the next command. For instance, c-X ( a b c c-U c-X ) inserts abcabcabcabc but the c-U is still there. At this point c-E (the usual next thing to do) will insert another abcabcabcabc instead of just abc.