Reproduction steps:
1. Open project attached(TileBug.zip)
2. Open scene "Test"
3. Press on New Sprite
4. Investigate warning under "Draw Mode"

Expected result: There will be no warning or it will say to change sprite mode to "Single"
Actual result: Warning says change mesh type to "Full Rect".

Note: Sprite has sprite mode set to "Polygon" and mesh type set to "Full Rect".

Reproduced on 5.6.0b3, 5.6.0b11, 2017.1.0a3