Steps to reproduce:

1. Navigate to any form that has selects that can be sorted (Items -> Preprocessing steps, Graphs -> Items, Icon mapping, Pie chart widget, etc).
2. Add multiple entries.
3. Open a dropdown.
4. Drag any element.

Also available as a video attached.

Result:
The dropdown is kept open and cannot be closed unless the selector is clicked on again, allowing to open multiple dropdowns at the same time and/or to hide the selector behind the dropdown itself, preventing the user access to it.

Expected:
The dropdown should close when attempting to rearrange elements.