Placing Slabs
You can't place a slab underneath an already placed slab
Created Issue:
Placing Slabs
You can't place a slab underneath an already placed slab
Moved Issue:
BDS-458 →
MCPE-41447
Added Confirmation Status: Unconfirmed
Added Affects Versions: 1.9.0 1.10.0.3 Beta
Removed Affects Versions: 1.8.1.2
Removed Affects Versions: 1.10.0.3 Beta
Added Fixed Versions: 1.10.0.3 Beta
Added Linked Issues:
clones
Added ADO: 174450
Added Linked Issues:
relates to
Added Attachments:
Added Linked Issues:
relates to

Moved to the correct project. Please update the affects version and platform.
I too can confirm this issue exists. To add further detail to it...
Prior to version 1.9, you could place slabs by right-clicking in the empty space on one of the containing walls as pictured in the screenshot. This is no longer possible, and you must always right-click in a specific place.

If you are trying to fill a space on top of a bottom-half slab, you must right-click on top of the half slab below. Conversely, if you are trying to fill the gap below a top-half slab, then you must click on the bottom of the slab that sits above the gap. This makes it impossible to fill a bottom slab gap in if you have a floor that you don't wish to destroy. It would be great if we could go back to the old logistics for placing slabs!
Affects windows 10 edition as well.