Incorrect geometry for slab generation

[exenGT]

I have found that for certain types of slabs, the geometry of generated structure is incorrect. For example, the correct geometry for LiF (111) looks like this: (generated with ASE surface module)

the same slab, generated with the "Make a Slab" functionality in Crystal Toolkit, looks like this:

Note that the Crystal Toolkit generated slab has a slanted supercell. Upon checking, the alpha angle is 92.3818 degrees, not 90 degrees as it should be. This behavior is also seen on the (111) slab of any rocksalt crystal (such as NaCl).