How to reproduce:
1. Open attached project "Case_1118608_tags.zip"
2. Open "SampleScene" scene
3. Open "Tags & Layers" (Edit > Project Settings > Tags and Layers)
4. Remove tag called "BE BE"
5. Add a new tag called "BE BE"
6. Select "Cube" GameObject
7. Change the Tag to "BE BE"
8. Build the project for Windows
9. Run the build

Expected result: Sphere is destroyed when it reaches cube
Actual result: Sphere is not destroyed

Reproducible with - 2017.4.19f1, 2018.3.3f1, 2019.1.0b1, 2019.2.0a3

Notes:
1) Testing in Play Mode in Editor does not produce the issue.
2) Restarting Unity Editor before building solves the issue.
3) Building the project for WebGL produces the same issue.
4) Javascript console in browser throws out "object has undefined tag" error.