schema.SingleNestedAttribute PlanModifier breaks other attributes

Terraform Providers Plugin Development
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I have added a simple object PlanModifier to a resource - add example of default causing issues by iwarapter · Pull Request #252 · iwarapter/terraform-provider-pingfederate · GitHub and its breaking other unrelated attributes.

Is there anything specific to using SingleNestedAttribute PlanModifiers?

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For future readers, this discussion was furthered in a GitHub issue: schema.SingleNestedAttribute PlanModifier breaks other attributes