I think the point is being missed here, as long as the slab is placed on the upper half of the block it occupies you should be able to place a bed on it. You can in fact place torches and redstone on slabs if the slabs are on the upper half of the block it occupies, this condition should exist for beds as well, it doesn't currently and is not consistent with other placement mechanics related to slabs.
EDIT: And I just realized this is bug is listed for Pocket Edition, nevertheless it's an issue with the PC version as well.
Warren Schnurr
I think the point is being missed here, as long as the slab is placed on the upper half of the block it occupies you should be able to place a bed on it. You can in fact place torches and redstone on slabs if the slabs are on the upper half of the block it occupies, this condition should exist for beds as well, it doesn't currently and is not consistent with other placement mechanics related to slabs.
EDIT: And I just realized this is bug is listed for Pocket Edition, nevertheless it's an issue with the PC version as well.