Issue (cosmetic): after slicing non-square sprites, they are shown as distorted square sprites.
(Note: the actual export files are correct)

Assets/settings used:

• Sprite sheet 31x51 pixels, 1 row, 3 columns.
• Slice settings:
  • cell size: 13x51
  • margin: 0x0
  • gap: 1x0
• Ignore tiles with solid color: Yes
  
  After slicing the result sprites are shown distorted as squares in the right panel:
  

I agree, it does look a bit crappy and it's not a hard fix, I'll sort it in the next update. Thanks for posting this.