Why do static pages rerender, including static content in ppr?

[mblandr]

Summary

I'm fist days in next. Here is my test project
https://github.com/mblandr/sample
When full page loading navigation begins from /about
/sample page rerenders every time, despite it is static, but /about doesn't
When full page loading navigation begins from /sample
/about page rerenders every time, despite it is static, but /sample doesn't
This is also for / page, if full page loading begins for any other page,
StaticComponent always rerenders, but when full page loading begins with /, it doesn't.
When ppr is disabled in config, no such weird behavior happends - all static pages don't rerender.
I don't understand this behavior of ppr, please somebody explain it.
Thanks

Additional information

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Example

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