How to reproduce:
1. Open user's project (test_bundle.zip)
2. Open scene "main.unity"
3. Play the scene
4. Observe the Console
5. Inspect "TestBundle.cs" script

Expected result: No async operation errors are thrown.
Actual result: Script cannot unload asset bundle because asset load operation has not been completed(Sync method behaves like an async one)

Reproducible with: 2017.1.0a3, 2017.1.3p3, 2017.2.2p3, 2017.3.2f1, 2017.4.1f1, 2018.1.0f1, 2018.2.0b1
Not reproducible with: 5.6.6f1, 2017.1.0a2

Notes:

• Delaying AssetBundle.Unload method by at least 1 millisecond circumvents the issue.