I've had following code:
<%= check_box "adsl_cpe_chk", "yes", {:onChange => "if (this.checked) { Element.show('adsl_cpe');} else { Element.hide('adsl_cpe');}"}%>
<select name="adsl[cpe]" id="adsl_cpe" style="display:none">
<%= options_from_collection_for_select @data_devices, :code, :name%>
</select>
and if I clicked (set) checkbox, the select field was still hidden - until I clicked somewhere else - with IE only.
I've discovered, if I replace onChange with onClick, it works ok. A few hours of trying everything are gone :(