Relative length units such as em and vw used in CSS calc() not working correctly

[MurakamiShinyu]

Test sample: https://gist.githubusercontent.com/MurakamiShinyu/f772284cdbf360387b0933a6474e5978/raw/em-and-vw-units-in-calc.html

<style>
@page {
  size: 50rem 50rem;
  margin: 5rem;
  outline: 1px dotted;
}
body {
  font-size: 200%;
}
p {
  outline: 1px solid; 
}
</style>
<p style="width: 20em">width: 20em</p>
<p style="width: calc(20em)">width: calc(20em)</p>
<p style="width: 20rem">width: 20rem</p>
<p style="width: calc(20rem)">width: calc(20rem)</p>
<p style="width: 50vw">width: 50vw</p>
<p style="width: calc(50vw)">width: calc(50vw)</p>
<p style="width: 50pvw">width: 50pvw</p>
<p style="width: calc(50pvw)">width: calc(50pvw)</p>

Test with Vivliostyle Viewer (v2.17.0): https://vivliostyle.github.io/viewer/v2.17.0/#src=https://gist.githubusercontent.com/MurakamiShinyu/f772284cdbf360387b0933a6474e5978/raw/em-and-vw-units-in-calc.html

In this test, width: calc(…) should be same as width: … (without calc()) but in the test result, width: calc(…) other than calc(20rem) are incorrect.