Suppose you have a select control with "multiple" property in $TCA (see the screenshot). You want to add the same item multiple times. You cannot do that by simply clicking the item multiple times: you have to click the item, the other item, again your item, and so on.
The cause: the control uses "onchange" handler. There is no "change" event when the same item is clicked.
The solution: the control should use "onclick" handler.
#2 Updated by Dmitry Dulepov over 8 years ago
TCEforms uses generic code for all kind of select boxes. Therefore changing "onchange" to "onclick" should be done with care. Possibly there should be two handlers: both onchange and onclick. Onchange would work for keyboard navigation in single select boxes, onclick will work for mouse navigation in multiple select boxes.