Smooth Stone Slabs are still called Stone Slabs, even though they should have been renamed.
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Thank you for your report!
We're actually already tracking this issue at MCPE-42390, so we will resolve and link this ticket as a duplicate.
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Confirmed in 1.11.0.3 on Windows 10.
Both the new slab with no border and the old slab with a border are called "stone slab" in the creative inventory.
In commands, the old slab is "stone_slab" and the new one is "stone_slab4" with a data value of 2.