I created a simple demo to confirm my problem:
- List "Filter" with items "Filter value 1" and "Filter value 2"
- List "Items" with additional multi-lookup columns "Filter1" and "Filter2" onto the Filter-List. Items:
- "Item 1", "Filter value 1", Empty
- "Item 2", Empty, "Filter value 2"
- "Item 3", "Filter value 1"+"Filter value 2", "Filter value 1"+"Filter value 2"
- List "Test" with additional lookup columns:
- "Filter" onto Filter-List
- "ItemA" onto Items-List
- "ItemB" onto Items-List
- Nintex Forms for Office 365 on Test-List with Responsive-Mode
- "ItemA" List Lookup Filtering Settings: By control "Filter" where field "Filter1"
- "ItemB" List Lookup Filtering Settings: By control "Filter" where field "Filter2"
Now if preview is used (or form populated), we can choose a filter and both dropdowns "ItemA" and "ItemB" always contains the same value. The requests sent contains only a single query to the Items-List.