Stacked items cannot be split / dragged in the inventory or crafting UI

Verification builds:
1.11.0.1 Beta | Windows 10: Yes
1.11.0.1 Beta | Android: Yes
1.10.0.4 Beta | Windows 10: No
 
Summary:
A stack of items cannot be dragged/split over the inventory or crafting grid - the stack just gets placed in one cell instead.  When using left click, it should spread them evenly. When using right click, it should split them one per cell.
 

Repro Steps:

1. Obtain a stack of an item, eg cobblestone blocks

2. Open a crafting table UI

3. Pick up the stack of cobblestone, and try and drag it over the crafting grid to split the items using Left or Right click

Observed Results:
The items just get placed in one cell, and do not spread. 

Expected Results:
When using left click, it should spread them evenly. When using right click, it should split them one per cell.

Screenshots/Videos attached: No

Notes: