Releasing left click while dragging out of the Tile Palette creates a phantom selection box

1. Open project
2. In Tile Palette, maximum zoom out
3. Click and hold anywhere on the Tile Palette, drag until cursor is out of the Tile Palette, release left click
4. Move cursor around in the Tile Palette

There is a phantom selection box created, bounded by where the user released left click while outside the palette.

Occurring in: 2018.1.0b1, 2017.3.0f2, 2017.2.0f3