Reproduction steps:
1. Open the attached project "TextUIBug.zip";
2. Open the scene Scenes/SampleScene.unity.
3. Click the play button and the script will flip the text UI between displaying:
A - "Alright...let's see what <color=#00000000>you got.</color>"
B - "Alright...let's see what<color=#00000000> you got.</color>"

Expected behavior: A and B versions should be rendered the same way.
Actual behavior: B version is rendered slightly differently.

Reproduced with: 2017.4.8f1, 2018.1.9f1, 2018.2.1f1, 2018.3.0a6.
Tested on both Windows and MacOS.

This is caused by the current text system forgetting about kerning sometimes while doing word wrap.

We will not fix this issue because:
1. The bug is subtle and should not have big noticeable effect
2. We will be replacing the legacy text system with TextMeshPro anyways
3. If we fix the bug, it will change how text is rendered and has backward compatibility concern