I still couldn't find any syntactical problem with the code, but on closer inspection, the logic of the code seemed quite bizabre (combination of bizarre and macabre):
It had a submit_button click handler that called $("form").submit();
If "submit_button" really is a submit button (input type="submit") - and it is!, why would that be necessary? Not only that, but the function called from the click handler had been declared this way:
$("#form0").submit(function() {
form0? What the Hec Ramsey?!? There is no "Form0" anywhere on the page...
Once I moved the code for submitting from the Form0 handler (which, I admit, I had previously changed from selecting the phantom 'form0' to 'form') to the submit_button handler, the much-awaited and yearningly longed for yellow background returned to the section's ending "}".
Voila!
Maybe the debugger is smarter than I thought: it goes on strike not only when the code doesn't compile, but also at times, apparently, when it (the code, or, by extension, the carbon-based biped who wrote it) a candidate for the loony bin.
Alas -- I know why the caged bird sings: he was trapped maintaining the code of birdbrains who had flown the coop!