The IPA.entity_select_widget could benefit from some improvements:

1. The "add <entity> filter:" label is not consistent with other labels. It should start with a capital letter like the Add/Delete label for multivalued text. The colon at the end should be removed because it implies that there is something after that.

2. The filter is not very intuitive. When the label is clicked it is replaced by a text field without any indication how the text field should be used or how it will work in relation to the drop-down list.

3. There is no clear way to reset the filter. The user could empty the text field, but he might be wondering if this is the same as never entering the filter in the first place. One solution is when the filter is emptied, text field should disappear and the label should be displayed again, so there is only one UI state that indicates no filter being applied.

4. When modifying the filter, each key-up event will trigger a call to the <entity>-find command which generates too much traffic to the server. This can be fixed by requiring the user to press Enter after entering the filter. Another option is to delay the execution until a certain amount of time after the user stops typing, but the UI may feel sluggish that way.

One solution for all of these issues is to have a text field that's always visible just like the search field in the search facet. The text field will contain a grayed out 'filter' text which will disappear as soon as something is typed in and reappear if it's empty. Also, there should be an icon (e.g. magnifier) indicating that the user needs to click it or press Enter to apply the filter.