See this Stack Exchange question:

http://emacs.stackexchange.com/questions/7443/mouse-problem-in-org-mode-export-window

The asker is trying to use the mouse wheel to scroll the org-export-dispatch
window. org-export-dispatch is using the built-in function
read-char-exclusive,
which in turn calls read_filtered_event with the parameter error_nonascii
set to
0. Unlike read-char, which will throw an error upon receiving a mouse event,
read-char-exclusive just keeps retrying, and eventually the echo area will
become full of mouse event names.

Here's the git diff of a small, possible fix for this issue:

$ git diff
diff --git a/src/lread.c b/src/lread.c
index 69ec059..0041b03 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -651,7 +651,10 @@ read_filtered_event (bool no_switch_frame, bool
ascii_required,
              error ("Non-character input-event");
            }
          else
-           goto retry;
+            {
+              message1 (0);
+              goto retry;
+            }
        }
     }


Nick Andryshak