Ensure that diff: ignoreChanges behavior is correct

[iwahbe]

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Issue details

We currently undo the "ignored" changes for Diff and Update. We need to confirm that this works as intended.

I have been told that the engine already handles this. We need to confirm if this code is necessary. If it is, we should put it under test. If not, we need to document the behavior of the engine and remove the unused code.

Affected area/feature