Sometimes (quite often) when opening a different syntax region --- a
quoted string, or block comment --- in C++ mode, the first character
after it gets eaten with some error message shown in the echo area.  I
managed to create a surefire (at least here) way to reproduce it.

* save the attached file as 'test.cpp' (it is quite large, but when I
  tried to shorten it substantially, error disappeared);

* start Emacs as 'emacs -Q test.cpp';

* issue Elisp command right at the start of the buffer with M-: (this
  emulates fast typing):

      (progn (insert "/*") (insert " "))

  note that two separate inserts are essential, with one "/* " error
  is not triggered;

* observer the following error:

      Debugger entered--Lisp error: (error "Invalid search bound
      (wrong side of point)")

Full Emacs version: GNU Emacs 24.0.93.3 (x86_64-unknown-linux-gnu,
GTK+ Version 2.24.10) of 2012-02-25 on gonzo

Paul