My users showed me the weirdest problem today. In my application is a select-box that allows users to select the classification. When the classification is changed, the div containing the icons for the actions (and the classification-select-box itself) is updated to reflect the new classification. So i use an observe_field to watch the select-box, and trigger some javascript to perform the magic. In Firefox this works perfectly. But my users tend to use IE8, for some obscure reason, and switching to FF or Chrome is ... difficult (What other browser?). The observe_field is written as follows: [ruby] <%= observe_field "mention_thm_classification", :frequency => 0.5, :update => "mention-actions", :with => "classification_id", :before => "Element.show('spinner_cl')", :loaded => "Element.hide('spinner_cl')", :complete => "Element.hide('spinner_cl')", :url => { :action => "set_classification", :id => mention } %> [/ruby] Pretty straightforward. The observe_field is contained inside the div that is updated. When in IE8 a new value is chosen, i get the correct value in my method first, and then i get a whole bunch of classification_id="null". I am guessing what happens is that when the html is updated, somehow also the select-box is emptied, and thus changed, and thus a new value is triggered. So i replace the html again, and the select-box is emptied again, and an endless loop is born. So, the easy solution should be: do not do the action of the observe_field if the value of the select-box is null, and that is actually really easy: [ruby highlight="3"] <%= observe_field "mention_thm_classification", :frequency => 0.5, :update => "mention-actions", :with => "classification_id", :condition => "value != null", :before => "Element.show('spinner_cl')", :loaded => "Element.hide('spinner_cl')", :complete => "Element.hide('spinner_cl')", :url => { :action => "set_classification", :id => mention } %> [/ruby] We add a :condition that checks just that! It still feels i am doing something wrong, that i should not have to do this, so i would be happy to hear any way to improve this.