Reproduction steps:
1. Import user's attached assets to an empty project ("Assets.zip")
2. Open "Sample Scene"
3. In Inspector window, select "TilemapWithExpectedBehaviour" instance and deactivate it
4. In Inspector window, select "TilemapDisplayingBug" instance
5. Open and select a white sprite in Tile Palette and try painting it
-- Sprite is being painted offset to a single line, stretched
6. Deactivate "TilemapDisplayingBug" instance and activate "TilemapWithExpectedBehaviour"
7. Try painting on the tilemap
-- Sprite is painted on a Tilemap surface, even square

Expected: Sprite is painted on a Tilemap grid depending on a mouse placement
Actual: Sprite is painted on a Tilemap grid offset to a straight line, independent on mouse placement

Reproduced with: 2017.4.19f1, 2018.3.3f1, 2019.1.0a14, 2019.2.0a2

Notes:
- Using "TilemapDisplayingBug" tilemap, issue reproduces using all orientations except ZX
- Using "TilemapWithExpectedBehaviour" tilemap, issue reproduces using only XY, YX, YZ, ZY

Fixed in: 2019.2.0a6