breakpoint is suddenly being ignored in IDE

[Mark E. Powell]

The subject line says it all:  breakpoint is failing to break script in the IDE (2.8.0 Windows XP).   As clean test, I create a new button with breakpoint followed by an answer dialog inside a mouseup handler.  The answer dialog appears without interruption.

Have rebooted.  Have searched docs for some mystery property that disables breakpoint.  No luck.

Any ideas?

Mark