Steps to reproduce:
1) Open the attached project.
2) Open scene 'Line Renderer Problem.unity'.
3) Play the scene.
- A trail renderer will be drawing circles, no line visible.
4) Press the GUI button 'Move Trail Renderer' to stop moving the trail renderer.
- When the trail is no longer visible, the line shows up. Pressing the button again hides the line and trail becomes visible.

Expected behavior: line is visible all the time.
Actual behavior: line disappears when the trail becomes visible.

Reproduced on:
5.4.0b18, 5.3.4b13

Did not reproduce on:
5.3.5p1, 5.3.4f1, 5.2.4f1