Bug Description

If you switch AMP mode, the validation cache is not invalidated. However, some validation results depend on whether the AMP page is the canonical URL, and therefore change between modes.

An example of this would be the change introduced in #3346, where a change from Transitional to Standard should change the excessive CSS validation errors from New - Accepted to New - Rejected.

Expected Behaviour

When I switch the AMP mode, I expect the changes in validation to be immediately reflected.

Steps to reproduce

1. Set mode to Transitional.
2. Add enough CSS to the page to hit the excessive CSS validation error on the AMP url of a page.
3. The validation screen will show that the excessive CSS validation error is marked as New - Accepted.
4. Change mode to Standard.
5. The validation screen for that same page will still show the excessive CSS validation error marked as New - Accepted - it should be New - Rejected instead.

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Acceptance criteria

Implementation brief

QA testing instructions

Demo

Changelog entry