Worked under Mozilla 1.3 as well. 1.5 seems to be a different story. Code involved was distilled down to illustrate the problem.

Ok, so I see the source of the problem stems from the fact that the input name and id have the same name. If I rename either one (but leave the other the same), it will work in 1.5 as well. Not sure why the behavior changed - whether it's by design or accident.