ID 351706 - [TAB] no longer spawns the Create menu in floating Layerstacks

Steps to reproduce

1) Open Example Head

2) Go to a Channel and view it in the Layerstack

3) Select a Layer and add a Mask Stack

4) Open the Mask Stack and drag it away into the main viewport, then pin it.

5) With your cursor over the mask stack press Tab to add a new Layer

Note: This is also noticeable when spawning Layerstacks via the Stack Icon in the Channel Palette

Workaround
You will need to dock the palette in order for this to work.

Reproduced by support
Mari 4.0v4 - Win 7, CentOS 7
Mari 4.0v1 - Win 7, CentOS 7

Earliest version tested
Mari 3.3v1  - Last working version

Expected behaviour
Clicking [TAB} when hovering over any Layerstack, floating or docked, should spawn the Create menu

Actual behaviour
No menu spawned.