Custom drop down not working

Since updating to UE4.17, any custom drop down menu will not display the list properly, instead the window will automatically close as you can see here: Screen capture - 1a81f10b889f5a661653bcffc5e6609f - Gyazo

Updating to 4.18 hasn’t fixed this problem and the only workaround is to select what I want from the content browser and use the arrow to apply it, which isn’t ideal.

Pre-4.17 the drop down worked perfectly fine.