Using the shoulder bash the Warden can make an unbreakable guard break. The situation is the following:
1. If the Warden hits you with shoulder charge he can make an unbreakable guard break.
2. If you dodge the Warden's shoulder charge he still can make an unbreakable guard break.

This bug allows Wardens to spam the "shoulder charge - guard break - heavy strike" combo to kill any opponent easily.

Why it is a bug?
The same mechanics with guard break after successful charge is a part of a strategy used by Justiciars, but their guard break can be countered and their charge can be dodged.