<UPDATE> 2016-05-20 Confirmed FIXED in version 77 - Thanks!>
<UPDATE> 2016-04-24 This problem is still present in version 75. </update>
The add new item dialogue has recently been improved. However, at some point, a bug appears to have crept in. Pressing the down arrow in the wikitags box correctly brings up the multiple-value selector. However, any values selected here are not copied into the dialogue box and are not recorded as new values with the item.

Comments
Fixed: Add item dialog: Wiki drop down does not fill textbox correctly
However, this entry is dropped from the list of changes actually made in version 76.