Personally I blame the documentation and the template defaults, or to be more precise, lack of thoroughness therein (and being involved in both documentation and template maintenance, I guess I'm entitled to do so :-)
Specifically, each of the display elements supports multiple <On ...> actions. Chooser (as well as all other input display elements such as Text/Number/Date Input Field) support both <On Click> and <On Change> actions (also <On Browse>,<On Focus>,<On Blur>, and more).
<On Change> is activated when the value in the field changes. <On Click> is activated when the field is clicked, and only when the field is read-only.
We are working on rectifying this situation by providing better defaults and detailed documentation for templates.
For best results, use the Firefox browser..