When I try to place a copper slab on the upper half of a block it automatically places it on the bottom half and if I try to place another slab on it, they don't combine into 1 'block', it places it on the block above it (in the lower half) or in the block next to it (in the upper half).

I have tried other slabs and they work fine, I also logged off the world and back on again as well as relaunching minecraft and the issue persisted.

Sorry if I didn't explain this well, hope you're having a good time