Hexagon tiles get distorted on changing values of the cell gap

Steps to Reproduce:
1. Create a New 2D Project
2. Right click on Hierarchy window > 2D Object > TileMap
3. Select the Grid Game Object
4. Select "Hexagon" option in Cell Layout
5. Change the Y values in cell Gap property

Actual Result:
Hexagon tiles get distorted

Reproduces on: 2018.2.0a4, 2018.2.0a3

Environment:
Occurs on Windows 10, Windows 7 and Mac OSX 10.13

Note:
Hexagon tiles are introduced from 2018.2.0a3.