Bootstrap ui lookahead dropdown only works after deleting selection first

Question

The software I am debugging uses ui-bootstrap-tpls-1.1.2.

By default, if I open a modal and then click on one of the text boxes that has a a lookahead dropdown menu, the dropdown menu opens.

If I then select an option from the dropdown and click on that textbox again to pick a different option, the dropdown will not open this time, unless I delete at least one character from the original selection.

How do I get that dropdown menu to open every time I click on the text box, regardless of whether something has already been selected?

thanks

Things I've tried:

onclick="TextBoxName.Text = String.Empty;"

onfocus="this.value=''" 

Clearing the textbox is not necessary, but I couldn't find anything in the documentation that would provide another way to accomplish this without clearing the text 'onclick' or 'onfocus'. Neither of those two functions above gave the result that I had hoped for.

The code for the modal:

below is a pick of the modal.

The red circle shows a textbox where a selection has already been made.

If I click on that textbox again, the dropdown will not appear until I delete at least one character from "2017/18 Items":