To reproduce:
1. Open attached Unity project "Trailbug.rar"
2. Open "trailTest" scene
3. Inspect trailTest.cs script
4. Go into Play mode and press space button

Expected result: moving cube should leave its trail from the very beginning
Actual result: cube only leaves trail after moving 1 unit (if you adjust the script to move 0.5f instead of 1 after each press of the space button, the trail will only show up after moving the cube twice)

Reproduced on: 5.5.4p2, 5.6.4p4, 2017.1.2p4, 2017.2.1f1, 2017.3.0f2, 2018.1.0a7