breakpoints being ignored

[Mike Kerner]

Explain this one:
8.1.3
create a stack
put a button on it
add some script
click in the margin to add a breakpoint - it shows grey with red border
run the script
breakpoint doesn't activate
Add a "breakpoint" line as the first line in the script
execute again
breakpoint still doesn't fire.

-- 
On the first day, God created the heavens and the Earth
On the second day, God created the oceans.
On the third day, God put the animals on hold for a few hours,
   and did a little diving.
And God said, "This is good."