1. define a math-macro \bs{#1}=\boldsymbol{#1} (the bug works only with the macro, not with the original function). 2. Go into math-mode and write e.g. "a" 3. Go with the cursor in front of "a" and type "\b" and then <space>, so that the latex-command remains unfinished. 4. Go back with the cursor one step (entering the latex-command) and complete it to by typing "s" to the complete "\bs" 5. press space again and you see that the command "\bs" will eat the symbol "a" that is following, and produces a bold "a".
* This is in contrast to what should happen (namely a \boldsymbol-box in front of the letter "a") and what happens if you either type from the beginning (without interruption) the complete macro name "\bs" or when you use \boldsymbol instead of \bs. - Sebastian