To reproduce:

1. Open the project, attached by the user (Tapper2018.zip)
2. Open the "SampleScene" scene
3. Enter Play mode
4. Observe that each frame the text is written on top of the previous frame and thus the text becomes a mess

Expected: each frame the text is clear and only the current value of the text is displayed

Reproduced in 2017.2.2p4, 2017.3.2f1, 2017.4.3f1, 2018.1.0f2, 2018.2.0b4, 2018.3.0a1

Resolution: This is working as intended. The scene's Main Camera's Clear Flags property is set to "Depth Only" which means that each frame is rendered on top of the previous frame without clearing anything but the depth buffer. Using "Sky Box" or "Solid Color" instead resolves the issue.